sansa and ianthe..........well sansa says she's a just stupid idiot girl from a stupid idiot world who can't possibly be expected to know about earth traditions and tries to leave with a cutting passive-aggressive remark
sansa is doing 4d chess meanwhile ianthe is drinking copious amounts of eggnog and trying to repress the memory of john making out with "one of his duplicitous sluts" (or worse, gideon and harrow kissing) in the next room and mentally practicing her next evil monologue. she'd probably end up kissing sansa and then biting her. for enrichment.
anyway sansa thinks it's less likely that ianthe suspects her of anything and more likely that she is just trolling for information like littlefinger might do, which is not better
i think the funny thing about sansa and ianthe's cr is that if sansa actually outright asked about john's secrets, ianthe is the only one would just share her notes no questions asked. she did with anna. sansa's attitude toward the whole thing and, in her opinion, arrogant assumptions about things she really didn't know much about just kind of peeved her.