Literally the only thing she'd need from Ruby or Sapphire is the infinite supply of magical energy, their most basic and automated function.I wouldn't say she needs to do that.
Ruby won't have trouble working with Medea, it's just that she wouldn't be able to use Second Magic things installed onto Ruby. Ruby can use them to a limited extent on Medea's behalf, but it just locks out Medea munchkin'in the hell out of Ruby.
And I meant more that she could do stuff like override Ruby's attempts at trolling and stuff. Force it to actually behave itself.