They change constantly, barsel... and I can't imagine you did anything wrong. I breastfed four, totally, without bottles. They definitely didn't need anything else, and tbh, I think if I had given them water, they would have been less thirsty, missed out, and maybe reduced the milk supply... bottle feeding may be different.
I also started weaning mine at about 4 months (one at 10 weeks), where now, it is 6 months minimum. But babies don't read books... they are ready when they are ready...
I just wish her and her mum all the best and hope they quickly work it out x