How is she with sippy cups/straw cups? I know it’s not ideal but your mum could use either one of those or syringe feed her maybe?
I would suggest trying lansinoh bottles if you haven’t. They have soft nipples so breastfed babies really like them. It’s the only ones my once breastfed baby drinks from.
Tommee tippee (baby likes that one) it's breast like and the como tomo one is too. Maybe talk to your friend about baby being near by?
What bottles did you try?