Number one...I have no idea why she would have an "O". I have to tell you that I haven't looked that close at mine but I do think they all have a slit. That sounds kind of wierd but I don't know if it means anything is wrong or not.
As for the food she needs to eat soon. Four days is a long time and she may just need some help getting started. I would try some of the Fancy Feast brands, especially the ones that are sliced because they are full of gravy. She may lap that up as a beginning. If not I would get baby food, I think everyone talks about veal, and feed it to her with a syringe if she won't eat it on her own. You may have to force her but she is going to get sick soon if she doesn't eat. There are a lot more experienced people when it comes to this so I hope they can advise you better than me. Do you know for a fact that she is drinking? Is she using the litter box at all?
She is probably grieving and may be one of those very picky babies that wants only the food that she is used to. Since that is unknown you may not have a choice but to force her. I know you don't want to and I hope you don't have to. I wonder if her teeth are ok? She may have problems and can't eat the dry. It's so hard to know.
I hope and pray that someone is looking for her!! How could anyone have thrown that baby away??