My point was that she tried to do so, even if near the end of the chapter, to get into a mood where it would be more natural to talk about it. She even says that's her plan from earlier on.
i would believe it would be even more jarring for him to hear her talk about that stuff from the get go, being as sensible about those topics as he is (not only from his upbringing, from what you're saying too). So trying to at least not be so abrupt with it is a valid thing in that scenario, lest Tadashi just runs and she gets the wrong idea about it (we as the audience can understand Tadashi would run from the shock and surprise of it all, but still end up wanting her regardless, but she'd just feel like she fucked up as badly as she could and start distancing herself from him thinking he hates her now or some similarly stupid thing, as it has happened before).
She at least was more honest in her words while being on that beach, if not direct, so I'll insist it was Tadashi who ended up making her stop from denying her so strongly. He could say that even if she looks good with it on, it would be better if they didn't go further and made some other excuse instead. Anything but the pure denial to her advances that he does there. Which he KNOWS is something she's sensitive about: she told him as much during the last chapter.
The crux of the issue being: why, when you're a couple that love each other as much as they've shown so far, would he think she wanting to excite him specifically is something negative? He definitely responded that with a lot less thought than he should have, and ended up making a mistake. It is an understandable mistake, but with everything that has happened it IS a mistake on his end regardless.
I do hope they properly talk about it next chapter at least. They're trapped in that island until the next low tide, and I don't want more than half a chapter worth of drama out of this dumb and easily workable situation. Sex or no sex IDGAF, I just want them to properly talk about it and both of them to state their stances on more sexy stuff at bare minimum, start softening Tadashi on that end so we can progress onto some better stuff.