Story highlights The child was involved in an ATV accident four months ago

A pool party was held over the weekend

(CNN) Four months after a catastrophic accident, Jamie Lynn Spears' daughter has reached a milestone.

Maddie Aldridge turns nine Monday, and the family celebrated over the weekend.

Spears posted pictures from the pool party on social media.

"Today was the perfect day for a party," she wrote. "Thanks to everyone for coming out, and celebrating with our baby girl

Today was the PERFECT day for a PARTY💜💛 Thanks to everyone for coming out, and celebrating with our baby girl💜💛 A post shared by Jamie Lynn Spears (@jamielynnspears) on Jun 17, 2017 at 2:57pm PDT

Also, I have to say a special thank you to @mallyb86 for introducing me to @signgypsiesnorthshore 👍🏻 Everyone was so accommodating, and these signs made everything look 10x better💜💛(this is not an AD, they were just truly amazing) A post shared by Jamie Lynn Spears (@jamielynnspears) on Jun 17, 2017 at 3:02pm PDT

In February, the child was steering an ATV to avoid a ditch when she drove into a pond on the family's property in Louisiana.