hi and thanks for your replys

she is with me for 4 Nights, mum 5N, me 2, mum 3.
I don't really understand. Does that mean it changes all the time? If it does, I think that would make living between two houses even more unsettling. At least if it's the same each week, she would know, "ok, today is tuesday and I stay at mums", or however it rolls. I think it would be easier on her to have an arrangement that is the same each week.

Perhaps you could concede a day, and try something like Thur - Sat with you and Sun - Wed with mum?