[Dark Paladin X]

Originally Posted by hinakatbklyn

She (Michelle Ruff) hasn't voiced too many characters with a cute voice these days, but she has before and I think she can do it again as Yui.

Backing on your statement, she does have a large vocal range and Michelle Ruff did a cutesy voice before.

Spoiler for one of other Michelle Ruff's VA works:

Tsukasa Hiiragi from Lucky Star is your best example here.

Another reason is that despite not being typecast into particular roles, she doesn't seem to have a lot of lead character roles.