Have you tried nursing her?
If you are concerned about her fluid intake and nothing else has worked, you can use an eyedropper. It will take a while, but it works (my daughter had to do that when dealing with breastfeeding and her son's nipple confusion).
There is also a site where you may find information on this; www.breastfeeding.com. It is by moms and for moms, and of course; they recommend breastfeeding - but you still may be able to find some answers there.
Also, have you changed formulas? Or is your water perhaps different? It is possible that she is able to discern a change in taste and that is what is making her refuse it.