Are you getting married? If not then bicycle storage is the least of your worries.
Cohabitating and combining assets without marriage is a recipe for disaster and "Several months" is not long enough. If you are "hitting a pothole" over where to store bikes then there is a fundamental problem with this relationship in the first place.
She is right, of course. Bicycles are not children. This should have taken about 0.003 milliseconds for you acquiesce.
-Tim-