Maybe she's not as passionate about it as he is. My wife was pretty far left when we got together, Obama voter and all, but now she's more conservative than I am. I think Trump's populism won her over, she is actually strongly pro-choice, but that just isn't a deciding issue for her. Many of her friends from Eugene where she lived for many years are very far left and she maintains strong friendships with them. The reality is that if two people are committed to a relationship it can work despite many differences.
My girlfriend is left of center and I’m right of center but we still get along just fine. We’ve had a couple interesting political conversations and differences but most things we agree on. Big difference between pretty far right vs left obviously.