I think it'd depend on where you wanna take her relationship w him. If it's a light one-sided crush then I don't think the age would matter. But if you want her to pursue a romantic relationship with him in step 2 (where he's 17 and a senior in HS), she'd def have to be older than Qiu/Tamarack age (14) since he sees them as children (so realistically dating wouldn't happen). Personally I wouldn't go any lower than 17 cause junior/senior dating is a no in my books, but it's honestly up to you and how you think their dynamics could play out.
But overall more love for our local black and white fanatic is always good!