I'm assuming there's a good amount of metal in the arena. OP never specified where the battle takes place, and Mags is pretty dependant on his surroundings.
Anyway, Mags has to act on an object in his surroundings first, and then use that object to attack Scarlet Witch. SW can directly TK Mags so she should be able to get off an attack quicker, and Mags has no way to block her TK. This is a win for SW.
God I hope Marvel retcons her relationship with Mags back into existence when they inevitably get the X-men rights.