Perhaps we are at cross purposes. I dont think that MARY is making a pun about homosexuality. I dont think she's quite that "louche"... I think though that Austen may have been aware of the issue and may have been aware that there was an even naughtier pun than about "vices"...

Of course it is impossible to know for sure, but I think that since Austen was born in the Georgian era, which was much cruder than the Regency and much much cruder than the Victorian age, even country gentry's daughters or parsons' daughters woudl be aware of various forms of sexual misconduct, even if their sea going brothers might not have used the coarser terms for them..and if she knew about heterosexual affairs I think she mgiht also know something about the things that sailors were said to get up to...
. I think that the Austens were an easy going family in many respects..Austen's father didn't mind her reading Tom Jones IIRC and he seems to have helped her try to get published.. and he was not agaisnt private theatricals. and clearly they laughed over her juvenile stories which were often about drunknenness and sexual misconduct and they might not scruple to josh and laugh about such things in their private family circle at least when they were younger...