It's still early on in their sexual relationship and Fem!John (or Molly) really wants Sherlock to perform oral on her. She deduces that Sherlock is reluctant to because he has a difficult time not thinking about the cleanliness of it. Fem!John is disappointed and a bit offended, because WTF, does Sherlock think she doesn't have good hygiene and spontaneity is part of what she likes about sex and she doesn't obsess over every little thought about how clean he might be so what the hell?

But then Sherlock just very matter-of-factly tells her that there's no reason to be upset because he has every intention of giving her what she wants. He then proceeds to undress her and takes her into the shower, soaps her up and massages her from head to toe, very thoroughly worships and washes every little bit of her until she's squeaky clean, fingers her until she's really fucking turned on and then takes her to bed and goes down on her until she comes a couple of times. Fem!John is quite ok with this turn of events.