Oh how frustrating! We had this problem with my son at 7 months of age, and my daughter was finicky about taking a bottle around 16 weeks of age, but she got used to it. I'd say it sounds like a reaction to going back to work, which is a change in routine for her. Is there anything different you have done? Ie fresh pumped milk vs. frozen, for example? I found that with my daughter introducing the bottle with very freshly pumped milk (like I'd pump an oz or two and then leave the house for my husband to give it to her) worked ok. And from there we worked up to stuff that had been stored for longer and larger quantities. Also, of course be sure you're out of the house or minimally out of sight and earshot of her when she's getting a bottle.
Ultimately we were never able to get my son to take a bottle once he want on strike, but fortunately he had started solids at that point so I just told our sitter to feed feed feed him, incorporating as much pumped milk into his food as possible.
Good luck! Going back to work is tough no matter when you do it.