Well, she had the same outfit and used extensions to get the hair right, but I guess facially they're meant to be the same?
Ultimate MJ could look pretty striking when she wanted to. I remember that time she dyed her hair black and dressed really skimpy for a party and then when she went on that date with the Molten Man band leader after she and Peter broke up (the 2nd time).
I only assume she'll be an antagonist because of her personality, abrasiveness, and how McGuire views MJ compared to Gwen.