I don't think it matters one way or another whether Val is a "self-insert" or not. It's all the same in the end. I think that more often than not when a dev labels something as a "self-insert", it's more how they'd like to imagine themselves rather than how they actually are. More like a wish fulfillment or a weird kind of role playing. So really it's a fictional construct one way or another just like any other character in the story.
I think she's a good character. I enjoy the flirting with the MC. My top three favorite girls are Val, Layla, and Mel's booty because they all have such good chemistry with the MC.