Random Thoughts.....What Are You Thinking?

Her relationship with Mistle starts out as one sided molestation and eventually becomes reciprocal physical interaction, but it's never really implied that there is an underlying emotional attraction from either girl, particularly with how quickly Ciri forgets about her in favor of Hotsporn. The first time Ciri is seen to be emotionally invested in an individual is Hotsporn, but he gets killed "before he can become her lover". It is assumed that Galahad would also have become an emotional+physical lover for Ciri, but the books never go far enough to know how far it goes, and the games skip over all of this entirely and seemingly imply that either Ciri's character shifts and becomes more dominant (she initiates with Skjall) or gained a lot more sexual experience in her time between realities. We'll never know which since Sapkowski has no interest in continuing CIri's story and CDPR is moving on from The Witcher.

So she could be bisexual, or she could be straight and have had a confused incident with a very sexually active female. No one can really say for sure since it is left somewhat undefined and is written more like a teenage girl going through the motions of finding her sexuality more than a definitive "this woman is bisexual".