She can’t do that without absorbing the victim’s memories and personality to the point she can barely tell which were her own, which she really doesn’t enjoy.

Plus, she also absorbs any abilities and powers they have… which, to be fair do come with a manual of sorts (the aforementioned memories and personality), if she can get past the confusion… but doing it with Ororo Munroe might be too risky, since any loss of control could lead to her unwittingly killing everyone around her, and / or messing up the weather for the whole continent…