can i take control of rebuttal with my rebuttal in a Mel mirror matchup ?

Yes. Rebuttal's [A] branch gains control of a spell — that's not countering, so empowered Mel's "your spells and abilities can't be countered" doesn't stop it (FAQ #11743). Their Rebuttal is a legal target (Energy 1 ≤ 4) and both are [Reaction], so you can respond on the chain and your Rebuttal resolves first (LIFO), letting you take control and make new choices for it (FAQ #11744) — even pointing it at a new target.

What the mirror does kill is the "otherwise, counter it" branch: any Rebuttal resolving without [A] just fails to counter a Mel-protected spell, which stays on the chain. So in a Mel mirror, Rebuttals still steal — they just never counter. Note that when you resolve the stolen Rebuttal under your control, you'll again decide to pay [A] (keeping/redirecting its target) or not (the counter fizzles).