Yeah, it's very possible with the right badge setups. Danger Mario is a popular strategy. You can also just get Zess. T to make you a bunch of powerful items. I'd recommend healing with crystal star power more than anything else, since it renews the fastest and you get tons of opportunity to grind it. (leave one enemy alive, defend, appeal, repeat)

My sister's the one who beat it though so I'm unsure. Maybe look up some strats for it, it's definitely hard and requires some planning.

I did. I didn't even use any gimmick strategy. Just did it near the end of the game, kept using Sweet Feast to stay healed.

Dang! that means my only problem is time! I'm always racked for time!!!