The two interpretations of the wife, which are fairly established here by now (unfortunate family protector vs egodriven whore), also apply to her "anal offer" to Hutch.
On the one side one can see it as a sacrifice of something she really doesn't like doing and derives no pleasure from, as an honest effort to rescue her marriage by working her ass off so to speak. It shows that she is mindful of his long-cherished wishes and knows that she has to stretch her limits. When I first played it I found it remarkable, because it's not a bad strategy (if there is one) in such situations at least in theory - no talk about: honey it's just sex, it doesn't mean anything, our love is strong, I'm so sorry etc. but straight to the point: it has to be dealt with and made good on the level of sex, which is of utmost importance to the man in that moment. There has to be a tangible compensation. And she shows an understanding of the male obsession with possession and exclusivity: when one path is lost, she has to open up a new one for him to feel exclusive again. Although of course the offer tastes a bit like medicine, given by a motherly nurse, not by a lover.
On the other hand it is just as clear, that she obviously knew all the time very well what she denied her husband for 20 years, how much he wanted it, and that she is only prepared to put it out if absolutely necessary, if cornered. The boy is sad, and we give him his toy at last to make him happy again. The moment it's of use to her she allows it. To get it this way must feel like a double humiliation for Hutch and what could be seen in the other interpetation as generous gesture appears like a cheap manipulation (and of course as the ultimate pity sex). She waited until it is too late and all lost. What he wanted from her of her own free will and even better in the heat of the moment (so he imagined it) she is prepared to give him as a kind of payment of debt (and with the clear expectation that he will be a good boy again after that). One could say, it shows a similar transactional use of sex as the one she has with regard to the boss (at least at the beginning).