Isn't working for me, neither Friday Evening event and morning and afternoon event.
It seems there are some additional conditions, indeed:
The first time you must talk to Taisha on the afternoon, when she is outside or in Dereck's garden and when it's not raining (i.e. she must not be naked). It's neither not possible if she is in the stable.
Talk to Taisha, then she'll begin to speak about her dress and that's it.
Then the additional 'Flirt' option (i.e. repeatable cleavage scene) will be available each time you talk to her in the future, as I've described in my former post.
I'm also almost sure that the Topless Friday scene for her is only possible after you'll have completed the Cleavage scene first (as she is also speaking of her dress during the dialog for the Topless Friday scene).