Yes, you can use Diona in melt teams or reverse melt if you want to. However, the caveat is that her Cryo application isn't that good regarding those team compositions. You have better Cryo characters like Rosaria, Kaeya, or Chongyun who can fulfill that role. Another con about Diona is that her burst might miss a target and not be able to apply Cryo at all. That puts you at risk of repositioning yourself on the battlefield and chasing that burst.