Question! Has Jean Grey ever gone up against Scarlet Witch?
I don't think so? There was a time when Jeen read Wanda's mind and saw what happened in M Day and attacked her, but there wasn't much of a fight. Besides that I guess they also had a fight in the early X-Men issues when Wanda was in the Brotherhood, but I wouldn't really seriously consider that.
Yes, she did in original run!
Jean said she wanted to test her Telekinetic Power against Scarlet Witch Hex Power. In one of her courageous moments, she went rushing toward Wanda, hurling TK force while also making numerous things fly around Wanda keeping her off balance. This was back when they were still drawing Jean's TK power with dotted black lines.