Soooo, she got her ass whupped so she had Sakuya cut off her hair to use as a spell reagent? Except she's sad about having to do it? Is that the gist?

That seems to be the gist of it. She loves her hair, but needs it for spells, so a sacrifice has to be made.

I thought girl will only cut their hair when they have their heart broken. Love is the reason most of the time.

Mr. obake said:

(...) love is the reason most of the time

Well, we ARE talking about Marisa, aren't we?

It looked to me that part of her hair was ripped/blasted off from the fight. I think she came to Sakuya so she didn't have half a head of hair. If you look at the first picture,the left half of her hair (our right) looked ragged and some of it is falling out. She was making excuses as to why she needed a hair cut. In truth, she wants to keep her hair. She might even find great pride in it. Its hard for her to have it ruined.