I didn't think it was forced. We see plenty of guys in brothels, why not women? Would you call the shaving scene between Loras and Renly forced gayness, since they hadn't previously been shown to be gay? I hope I'm not being too snippy, I do get somewhat personally invested in the issue but I just don't like the idea that a character being revealed to be gay or bi out of nowhere is necessarily forced, since it depends on the idea that everyone is straight by default. Certainly it can be forced sometimes; if they revealed Sansa to be into girls after all these seasons showing her attracted to guys with nary a peep of lesbianism it would be quite forced. But the show doesn't seem to have spent much time on Yara's love life, aside from her teasing Theon which doesn't really count (I haven't watched every episode so please tell me if I missed something).

I forgot about Asha and Qarl's roleplay. I mean that could have just cut that part out and included her relationship with him. But I think you're right in that they wanted to include a lesbian character, and Asha's romantic antics were easy to sacrifice.