how the time-travelling girl would interact with her future girlfriend, back when they're just friends?
Most of us would like to keep everything under control since interactions with the past might cause a big impact to the future. That said, probably just let things happen as it already did.
On the other hand parallel universes is also a thing that haven't been proved yet... So if you don't care about the future and believe in this parallel thing... Might as well go "fuck it" and have your way with life.