9 month old not taking bottle

[Dreamalittledream]

My children were breast fed so I have little experience with formula fed babies. I have a 9 month old little one who I have had for about 9 days total she comes 3 days a week & there was 2 weeks vacay in the middle. So, this little girl's parents tell me that she has, on average 4 bottles a day (she gets one each time she wakes: AM, after each nap & 1 before bed at night). 1st week she took the bottles no problem. Since then she refuses (she bites the end only, doesn't even taste it). She's eating very well & I've resorted to getting the bottle (formula) in her by having her sip it from a cup (I know with some the sucking action hurts while teething). Frustrating because she still takes the bottle no problem at home. Having her sip it all from a cup is painstakingly slow, messy & is one thing I will do, but honestly don't have time for the 1/2 hour + it takes. I am also mixing the formula mixture that she doesn't sip into her food, so it doesn't go to waste & she's still getting the nutritional benefit. Any ideas?