Three weeks is a long time for it to still be in there. What is inside is rotting. You can try to pull it out, but as long as it has been in there it is highly likely to tear off inside of her and that's worse that what you have now. I would give her an antibiotic to combat the rotting mess inside of her. I would also give her a hormone which causes her to try to push it out. We have used it before, but I don't remember the name of it. Talk to your vet about it.