YTA. Your girlfriend is grieving the loss of her baby while also having responsibility over someone else’s child. Yes, she may have been more strict disciplining your daughter which isn’t fair on your daughter at all however she has realised that this is a problem and requested that you give her a week to help her grieve properly which is not unreasonable at all.

Your girlfriends actions and understandable, however it’s not fair to have your daughter around your girlfriend if it’s likely she will be treated unfairly. It’s also not fair on your girlfriend having the ultimatum of having responsibility over a child that is not hers while she is grieving her own or leaving. Give your girlfriend the short time she has requested to grieve properly and stop dismissing her pain.