I agree, keep a close eye on her - and what's in her litterbox. I do hope it comes out in the other end! Just a few ago I saw an operation on a cat who had swallowed a string, it can get quite serious if not taken care of.

All you can do to avoid this, is to keep all string, yarn, elastic bands etc. in a safe place. If she is young, she will tend to explore, so keep an eye on her.

One time, my cat was in the process of swallowing some yarn, but luckily I was there to see it, and I pulled it slowly out.

She may want some cat grass, try that!

Good luck - and welcome to PT.