My friends mom died 2 years ago and her half-sister has the ashes,(the moms half sister) since then, my friends dad had died and according to his will, everything is left to my friend.
She just needs to know if this includes her mothers ashes, as she desperately wants them reunited with her dads ashes.
Has she any legal right to her moms ashes

I would depend on how the ashes were handled when the mother passed away. If dad gave them to the sister, then they are hers and do not belong to his estate. If they did belong to him and now his estate, then whom they pass to would be governed by his will or intestate laws in your location. Your friend needs to find out how the ashes were handled when her mom passed away, but if her aunt has had them all this time, I would assume that it is because her father let the aunt have them.