First things first, don't pull! Chances are that the string is further inside of her than you'd think and it may lacerate her internally and require surgery.
There are two different ways to tackle this. First, keep an eye on her and ensure that she is still eating, drinking, urinating and defecating normally. Trim the thread where the end is still visible, but won't catch on anything. Allow her the opportunity to try to pass it normally.
The other route, and the one I recommend, is to take her to a veterinary office and allow them to medically manage her. Linear foreign bodies can be a very big deal and can claim the life of a pet if they are bad enough. I would reach out to your daughter, if you're able, and talk to her about what route she'd like to take. Usually, in this case, some high fiber food is indicated to try to push the foreign body through, but radiographs and barium study may be indicated depending on her condition.
If you opt to keep her at home and watch her, know that she will need to be seen immediately if any of the following occurs: vomiting, blood in her stool, cramping, sensitivity in her abdomen, inability to defecate, signs of what appears to be constipation, refusal to eat or drink, etc.
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