I agree that Lena probably will spend a good amount of the next episode visiting her parents – or at least enough time for something significant to happen. If she doesn't, it wouldn't really make sense for the previous episode to end the way it did. But I very much doubt that she'll spend the whole episode there, exactly because it would be so limiting for her potential sexual encounters, and because it would more or less pause her progression with everyone she's already involved with.
Early in the development of the coming episode, I think Eva gave an estimation on the number of scenes she were drawing. I can't remember the amount, but I think it was about the same number as the two previous episodes (around 10?). The scenes have been split more or less evenly between Lena and Ian up until now, and I assume it will be the same in this episode. Something that most likely would presuppose that she returns from the trip at some point.
When it comes to what could happen on her trip back home, I agree that a scene with Axel is among the most likely scenarios (or with Ivy, for the same reasons). But Lena's already got a pending photo shoot with Axel, and she hangs out with Ivy all the time, so Eva could just as well have written scenes with them without the trip back home. The same logic would apply for a one night stand: Lena doesn't have to travel somewhere else for that.