I don’t think it actually matters for the Witcher series. They don’t tend to dwell too much on the events of the previous game.
I assumed that Yen was something from the Witcher 2 (that I skipped), but I don’t think she’s in that at all. If anything it relies more on the books for the backstory of each game.
Witcher 1 is a very odd game, gameplay-wise, that makes more sense when you realise it was initially some top down D&D game. It’s just presented as a regular 3rd person game that we now expect to play somewhat differently, rather than the odd “click the mouse at the right moment” system they went with. It’s worth it just for the story. Just turn down the difficulty as it’s really not worth struggling with, although for me the hardest boss in the game was a dog near the start.