Focusing on what Harry brings out in Jasper rather than contrasting him with Bella is one way to handle it. Instead of making her a villain, you could frame it as her story ending before it truly began. She might be genuinely happy for them, or perhaps she and Harry were never meant to be in that universe, a simple matter of cosmic mismatching. The challenge, and the interesting part, is figuring out the trigger for the mate bond itself—does it snap into place the moment Harry arrives in Forks, or is it a slow realization that complicates the existing dynamic with the Cullens? Bella could remain Edward's friend, or even develop a separate, compelling arc exploring her human life without a vampire romance, which would be a fresh take in itself. The real conflict doesn't need to stem from her being 'less than'; it can come from the external threats both characters carry, like Jasper's past or Harry's magical enemies reacting to the vampire world.
I've seen a few fics attempt this, and the ones that work best treat Bella as a fully realized person with her own dignity. Maybe she's the one who senses the bond first and nudges Jasper toward it, showcasing her kindness rather than jealousy. That sort of character-focused choice prevents the story from devolving into petty drama and keeps the reader invested in the central pairing for its own merits.