Tldr - how to withdraw attention when we run into each other irl and she gets extremely upset?

This is one of the principles I still don't fully understand. The girl I'm with ranges from ok to fantastic 90% of the time and sometimes she's just in a shitty mood. I simply don't want to deal with that, even if it's my 'duty' (heard that enough times).

We're in college buildings right next to each other and it's very difficult to actually avoid her irl. Whenever I try to withdraw affection (which always works to my advantage) I end up falling back into talking to her. She cries, begs, and gives me everything I want after I do it. I've come to realise that sometimes I need to take a harder stance and push past that, but only if she disrespects me properly.

How can I actually do this without simply coming off as burthurt and not being able to take a bit of feminine hormones? It seems like more work than its worth if I know her shit won't last long.