Honestly, I read this comic as being pretty straightforward. Tai caught herself getting all hot and bothered over a girl she's not only friends with, but is a very recent ex of a guy she works and is friends with. Hence, guilt. The whole "Tai finds Dora attractive" isn't exactly new ground for us, it's just that while it was fun to joke around with Marten while they were dating, she knows it isn't all that funny anymore in the aftermath of a recent, painful breakup.
I suppose this may be the rare occasion of me not reading enough into the situation? But really I took Tai's comment at face value, calling a "not cool" on herself for inappropriate girlboners.