SAN DIEGO (KGTV) - A San Carlos woman's trip to the San Carlos library turned into nightmare after she was bitten by a dog.

A large bruise and two puncture marks remain stamped on Tricia Erler's left thigh.

"I was in total shock," said Erler.

On Tuesday afternoon, she had just finished a mind-and-body class inside the library, grabbed some magazines, and was headed into a lounge area to read.

"I was behind this woman's chair, and she got up abruptly and swung around in one movement ... she sort of fell into me, and I fell into the books. I felt a stabbing pain in my leg. I thought something had stabbed me from her backpack," said Erler.

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Erler limped to the front desk area and pulled up her pant leg.

"You're in total disbelief. You're bleeding and there are teeth marks on your leg," said Erler.

Nearby, she saw what bit her: a leashed white dog, possibly an Australian Shepard, with black markings on its head. Next to the dog was the woman who had bumped into her. She was in her 20s or 30s with a stocky build.

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According to the librarian, the woman claimed she was going to go to her car to get the dog's information. The woman walked out and never came back.

"I was upset and shaking. You would think you'd be totally safe in a public library," said Erler.

Erler just received her second of four shots for a rabies regimen. Back at the library, an animal policy is posted on the front door: only service animals allowed.

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"This proves we need better regulations. Definitely feel dogs should be checked," said Erler.

Under federal law, dog owners can be asked if the animal is a service dog, but can't be asked for documentation. A city spokesperson says their policy is to ask every animal that enters a library. In this case, officials say staff did ask and the woman confirmed it was a service animal.

Anyone with information on the case is asked to call the San Diego Humane Society at 619-299-7012.