Besides, it's Historia. She always feels embarrassed, she did the same when she was tending Reiner and having to rip her own clothes for it.
Historia still doesn't know why Ymir goes to great lengths to protect her, she had Connie and Eren reminding her that Ymir's actions were to protect her and only her. That's why a reunion is inevitable because their separation was so sudden and unexpected, they didn't even got time to talk. Even after Utgard, Ymir was still sleeping and then RB happened, so no time for talk either. I think Isayama is trying his best to cockblock them for some reason.
There is still this huge question mark about why Ymir is protecting her, she will either hear it from Ymir herself or from others.
But Ymir is such a stubborn person, she probably won't say it out of fear or something.... What do you guys think about it?