I knew there was a reason I never watched the newer movies...THAT'S Tonks?

But yes, at least in the books, her relationship with Lupin seemed to come out of nowhere and should have been better explored if it was going to be included.

One of my main criticisms of SS/HG fans who wanted that ship to happen in canon (besides '...really?') is this; there's no way a quest-centric Harry POV could show the reader enough of the relationship to do them justice.