NanaPlenty I feel sure something is going on with your daughter and it may have nothing to do with you - in the sense that you are not the cause of her being distant, not in the sense that it is not your business!
Please do the babysitting, just hang in there, you don't know what is actually happening. Be a quiet support. She is your daughter. When a member of a family is found to be becoming more distant by all the family, my first thoughts are, is she under the influence of a man who is controlling her and cutting her off from you all? He might seem like a wonderful person to you, but he could well be a dangerously controlling man indoors with her. Be patient and try not to put pressure on her. Don't lose touch, please. Even though you are not to blame, take it on the chin and say you didn't mean to upset her, that you just miss her and you'd love to see the children and look after them for her. Stay in touch. Be open, don't ask any questions or you will drive her away. But be there to support her in case there is a crisis.
I have seen this before, in case this all sounds a little over the top. I hope it is simply an innocent explanation, such as that she is a bit over-tired. However, I really want to urge you and her father to be patient, put up with her and be there for her, please.