Manga did a bad job of explaining it. Manga made it look like she was guilt tripped into accepting it, but it was really more like she noticed how sad he was by her rejection and being so bothered by how sad it made him made her realize she was still in love with him despite how much she tried convincing herself she wasn't, and so she consented because she wanted to be with him despite her belief he was actually in love with someone else.
There's some weird behavior going on as a result of some spoiler things that haven't come up in the manga yet

She would've fought harder if she didn't want to get rapēd?