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The star says her 21-year-old daughter's case was "extreme and caused serious anxiety and multiple phobias."

Lisa Rinna thinks she may know what caused daughter Delilah Belle Hamlin's mental health issues, which the 21-year-old model first spoke about publicly last week.

The "Real Housewives of Beverly Hills" star took to Instagram Monday to praise her oldest and her youngest -- 18-year-old Amelia Gray Hamlin, who recently revealed she struggled with an eating disorder -- for their bravery. Rinna then shared with her 2 million followers that she believes a childhood illness contributed to Delilah's condition, which landed her in rehab twice last year.

"First of all I want to say how proud I am of both of our girls," wrote Rinna, 56, speaking on behalf of herself and her husband, Harry Hamlin. "I am in awe of how brave and courageous they are!"

"In regards to Delilah's recent post, I think it's time to discuss the condition that started it all -- PANDAS," she continued, clarifying that the acronym stands for Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal Infections. "Roughly 10 percent of the pediatric population will develop PANDAS to some degree."

According to PANDAS Network, the disorder "occurs when strep triggers a misdirected immune response and results in inflammation on a child's brain. In turn, the child quickly begins to exhibit life-changing symptoms, such as OCD, anxiety, tics, personality changes, decline in math and handwriting abilities, sensory sensitivities, restrictive eating and more."

PANDAS Network estimates that PANDAS and similar disorder PANS (Pediatric Acute-onset Neuropsychiatric Syndrome) affects as many as 1 in 200 children.

In Delilah's case, Rinna says "the condition was extreme and caused serious anxiety and multiple phobias."

"Thankfully, we found the appropriate therapies and [over time] she is doing much much better," she added, encouraging parents who notice their children struggling with anxiety to visit PANDASNetwork.org.

On Friday of last week, Delilah detailed her experience with mental health issues via multiple posts on her Instagram Story. She did not, however, reference her childhood battle with PANDAS.

The model began by saying she decided to get candid with her 1 million followers in the hope of helping others who may have similar issues.

"I've been hesitant to share this information with you guys because there are a lot of you now and sometimes that scares me," she wrote. "I strive to try my hardest to be a positive influence on my younger followers. I wanted to share this with you guys today because it could help at least one person struggling with anxiety and or depression."

"This time last year I was in rehabilitation," she revealed. "I moved to New York to start my journey as a student at NYU. Not long after I moved to New York I began having terrible depression. I started attracting negative people into my life because my thoughts were so negative."

"I got trapped in a severely unhealthy relationship that pushed me over the edge," she added. "I couldn't get out of the relationship because I thought I was deserving of it."

Delilah explained that eight months into the unhealthy relationship, she "couldn't take the pain anymore," so she reached out to her mom in February and flew home to Los Angeles.

"Two weeks later I was admitted into a rehab facility," she recalled. "I knew the way I was living was unhealthy and detrimental to my mental health so I called my mom and told her I needed help. Little did I know this was going to be the BEST thing that has ever happened to me. I learned so much about being independent, feeling less shameful and guilty, I learned about self love instead of self deprivation and so much more."

The 21-year-old said she returned to the facility in June and stayed for 60 days.

"This experience was truly the best thing that has ever happened to me," she said. "I worked through traumas and self-love. But most importantly I learned what self-respect meant."

"Saying no is OKAY! Do only things that make you happy and make you feel good about yourself," she added. "Don't let another individual take over your life and tell you who you are or how to be. Take control of your own life and get rid of all negative people and energy that may surround you. And I guarantee this will lead to a happier life even if it's hard in the moment."

She concluded by encouraging her followers to ask for help if they suffer from mental health issues.

"If you suffer from anxiety or depression, or rather any of the things I've mentioned above, then don't be afraid to be VULNERABLE and ask for help because it will change your life," she said.

Delilah's younger sister, Amelia, opened up about her struggle with eating disorders on camera at the start of "RHOBH" Season 9. A later episode showed her at a family barbecue, refusing to eat what her dad had made. She came up with every excuse as to why she wasn't hungry and didn't want to eat.

Amelia knew criticism over her behavior and attitude toward her dad would be coming, so she preemptively explained herself and her "fear of food" on Instagram before the episode aired.

"PSA!!! Lollll tonight on the housewives you will see how my eating disorder affected myself and my family," the 18-year-old shared in a series of Stories. "There is a scene where I am EXTREMELY rude to my dad and the food that he wants me to eat. During that time, one year ago -- I was not in a good place at all."

"I may have looked like I was recovered, but I was most definitely not. Within the scene you will see me lashing out due to my fear of food," she explained. "The person displayed in tonight's episode is not the person I am. It was the person anorexia made me. I hope you guys can take this and relate to it."

"I'm sure I'm going to get thousands of horrible comments in regards to how rude I was to my father," she went on to accurately predict. "I just wanted everyone to know why I acted the way that I did. I was a vegetarian because I was AFRAID of eating meat. If you watch it you'll understand. Please, just know that this is an opportunity to witness my anorexia in full force."

At the time, Amelia said it was "hard" for her to "relive one of the hardest times of my life" by seeing it back on the show but said she's now "100% RECOVERED AND HAPPY!!!!!"

And, yes, she eats burgers on the regular now, "in case anyone was wondering."

Like clockwork, viewers called Amelia's behavior at the barbecue "disgusting" and said her mom was "responsible" for how her daughter acted. Someone on Lisa's Instagram page even commented, "You're the reason Amelia has an eating disorder."

Sharing a screenshot of the nasty comments her mom was getting, Amelia said, "Sorry but I have the best mom in the whole entire world!! Stop being so jealous! Hahaha."

She added, "HOLD THE MOTHER F--KING PHONE PEOPLE R SO FLIPPING FUNNY. TELL ME YOUVE NEVER BEEN A BITCH ONCE TO YOUR PARENTS. TELL ME PLEASEEEEE."

The backlash and negative comments kept coming, as Amelia said in another Story, "Some woman just told me I don't look anorexic...this world is pushing my buttons. SOMEONE HOLD ME BACK." She then went on to share two photos of "what anorexia looks like," explaining that "there is not just one type."

Although Amelia is on a good and healthy path today, she recognizes that dealing with eating disorders is sometimes a lifetime commitment.

If you or someone you know is struggling with an eating disorder, visit NationalEatingDisorders.org.

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