I really like their whole vibe. I think initially Sancho would get supremely insecure about things because she'd see Don Quixote, the one person she'd ever consider to be trusted and loved, to be getting closer and closer to this strange, persistent woman who he keeps clashing with. Yet, she can't help but be intrigued by her as well. Bari is as patient and consistent with Sancho as she is with Quixote, and it would gradually endear her to Sancho.
And even after they were forced to flee La Manchaland, Bari never left her. She was always by her side. Even after Sancho wanted to forget it all, Bari always respected her wishes and just wanted her to be safe and happy.
It's a love bound by consistency, above anything else. The knowledge that Sancho can rely on her always, in presence or in spirit.