Originally Posted by
SpoonyViking
Mostly, how completely different she acts during the threesome in Fate and during her own sex scene in UBW (or even in UBW's Good Ending; while she makes it clear she's the "owner" of the harem, the sex in itself is only mentioned in regards to Shirou and Saber, not herself and Saber).
Basically, while I wouldn't categorically state the character isn't bisexual, or doesn't show attraction to others of the same gender (she's pretty smitten with Saber, and she does comment on Rider's beauty in a way that can be read as more than platonic),* I feel the only explicit same-gender sexual leanings she displays is in Fate's first H-scene, which is basically an anime-fied " 'Sorry, mister delivery man, I don't have a tip for you!' 'Oh, but I have a tip for you! [BOW CHICKA WOW WOW]".
* Particularly when we contrast to how other characters are written; Issei, for instance, while also awed by Saber, describes her not in terms of beauty, but holiness.