Try not to stress. Thousands of moms have gone down this path before you, and chances are good that baby will learn to take your milk just fine while you're away.
To make the transition go more smoothly, it's probably a good idea to start getting her used to a bottle two or three weeks before you head back. Substitute a bottle of expressed milk for a feeding once or twice a day to get her familiar with it. Know that different babies do best on different bottles and nipples — buy a few and see what works for you before investing in a full stash of one particular brand. If baby has trouble taking a bottle from you, let your partner (or another family member or friend) feed her your expressed milk while you pump. (Some babies don't like taking a bottle from mom or even when she's nearby. They know there's the option of a breast and would prefer to drink straight from the tap.)
Rest assured that if baby simply can’t get the hang of the bottle (which is not likely), she can always be fed by cup, spoon, or finger-fed.
Just don't forget to pump every time baby takes a bottle. This will keep your supply up and help build your stash for baby.