Yeah you don't need to 100% her, even in Europe. I think it relies on key moments where it is a choice between her and Chris. You can take Riley home from the party, and you can also take the Underground back from the bank in London and take Aubrey back to the hotel when she sprains her ankle in France. Just always support her over Chris in any choice or conversation and sneak out of the museum see the clocktower in London and you should be good. I had no problems getting her on a couple of different playthroughs.