I have 2 kids who were both resistant to bottles, my daughter finally started taking one bottle a day at about 4 months, after us trying 6 different brands/nipple styles. My son took till he was 6 months before he would take one AT ALL!!! Finally I had to "force feed" him, basically, held his arms down to his sides, put it in his mouth and rocked and sang constantly while holding it in his mouth....he finally took it and after that it was easier.
Like others said, it had to be really warm, like body tems, and they had to be held as if they were nursing, really close/tight to my body, and kind of on their side a little. Also, you could try to trick her and feed her in her sleep - that also worked better with mine.
The bottles that finally worked with both of them were MAM/Sassy brand, here is all about them - they have a different, flatter nipple, that is textured, not smooth shiny, just like a breast nipple flattens in their mouth, also BPA Free, anti-colic/gas design, and the newest ones are self-sterilizing:
http://www.mambaby.com/mam/the_products-drinking-bottles,...
The kids would NOT take any others, and even once they were bigger and would try to drink out fo a regular one, they would drool and leak milk all over themselves, never dripped one drop with these!
Good Luck, I too think this was mom's job to tget them to eat from a bottle before taking them to a caregiver....but too late now. I think you should talk to her, have her buy the bottles and work on it at home, too. Remind the mom, if the baby won't eat all day with me, she will be waking mommy up all night ot nurse to make up for it!!! Also, I know she is young, but you could try a sippy cup ( without a valve - you would have to tip it to giver he one sip at a time), ot a tiny open, dixie cup, it would be faster flow and she wouldn't have to suck hard...but would get something out of it, so she isn't starving.