turns out the artist posted an apparently redone version on their pixiv, so i went and read it!
i feel like a couple of lines could use more context with that, and it's very possible some or all of these were full writing changes between versions. the thing where (during her sex work) she suggested lube and the other woman got angry, the reason she got mad was because lube likely costs extra with the brothel. it's one of those paid add-ons? so eriko here messed up and basically was like "if you pay extra we can do it properly", which, of course that wouldn't go over well. imo it's less about her being a top or not (technical skill) and more about her attitude and communication, which is suuuper important in any kind of sex. she also says the reason she got into sex work was that she was confident in her appearance/looks, which ties into the themes nicely.
the painting itself was still on display at the gallery, and it was shizuko that was like "if you wanna see it that bad just go", but the gallery was full of people and she wasn't able to find it before she overheard all that stuff and impulsively ran back. there are some smaller parts too (she was asleep by 7pm and not 8, the "can't believe i find you so charming" line is more like (teasing, flirty) "well aren't you cute?"), and a lot of the dialogue just being much more direct than this version implies. like her boss saying "you're ancient at 30" was more like "when you hit 30, you're an old woman (derogatory)" (fill that in with your misogynistic language of choice). very effective.
lastly, a neat detail that's impossible to translate! eriko's name is written with katakana (meaningless) for her coworkers etc, but shizuko's dialogue uses the kanji: 英 (in this case is probably "outstanding", and not great britain or the english language (lol)) 理 (reason, logic) 子 (in both, common ending to girls names). so like, while everyone else is only addressing the surface, shizuko is seeing who she truly is! and while i'm at it, her kanji: 志 (resolve, ambition, hope) 寿 (a long time, lifetime) 子 :3