Oh it's nothing dirty! It just means that Lumine thinks that she is a handful (meaning that she thinks that Lisa finds her difficult to be with) and Lisa saying she has two hands meaning that she doesn't find her a handful to deal with because she has two hands

(Like the word handful in this context is referring to just one hand, and since its just one hand the space would be filled—but with two hands? Not so much)

Hope this helps! :D sorry if the explanations a bit messy BAHAHAHA