Daisy has a good neutral against Roy with her turnips. Put on turnip pressure and force him to approach. If he tries to fair and catch them, run in and punish him for it before he can use them. Daisy also has a a decent dash dance game and a kill dash attack, so try to bait him out if turnips feel too risky. You can also fake a turnip pull by crouching, then dtilt into a combo of your choice or a tech chase. Roy doesn't have a projectile or reflector, so turnips are typically your friend here. He does have a counter, but its punishable, and you have a counter too.
Daisy