I had a bottle-refuser from 3mo. Had MIL and DH spoonfeed her breastmilk when I was away. At some point--about 4.5mo?--they started mixing some cereal in. Plus the usual purees. A little water in an open cup. She also took some straight breastmilk in an open cup, and eventually took a sippy as well (but not until about 9mo). You can try breastmilk in a straw cup--some people say straw cups are better.
It was quite a nice way to do things, really; I did leave some breastmilk of course, but felt under less pressure to do loads and loads of pumping and stashing. And it's certainly handy to have someone else "do the solids" most of the time during the early stages (solids are fun but soooo messy!).
No 'have to' about it. Bottle-refusing DS started nursery when he was five months and hadn't started solids, and we didn't wean until 6 months. You may find your DC is quite different with the CM and she will either be able to get her to take a bottle or (preferably) a sippy cup with milk. She'll probably only take the bare minimum for a while but will pick it up. Are you doing a lot of settling-in days before you go back? They've been a godsend for me because it gave loads of time for feeding and sleeping worries and issues to sort themselves out without me stewing away at work.