Wanda couldn't affect her probably because she wasn't strong enough to affect a 4D being. And GR is one, so her powers would affect him like they affected Jean.
There’s a bunch of assumptions in here
Jean Grey first of all isn’t a 4D being
Second there was a little random girl who also wasn’t affected by the Wanda remember and she wasn’t a 4D being
third it’s not stated the reason why Wanda never affected Jean
fourth none of this has any bearing on offensive ability. Wanda did this reality warp semi-accidentally and without malice so none of this can scale to what she can do INTENTIONALLY with MALICE