One way is to look for fanfiction communities that have strict rules against adult or inappropriate content. Reddit has some great sub -reddits dedicated to Marvel fanfiction where users often recommend clean and interesting stories about Jean Grey. You can also ask for recommendations in these communities.
Try searching on official Marvel fanfiction websites or blogs. These are more likely to promote family - friendly content. Additionally, you can follow some popular Marvel fanfiction authors on social media. They often share their work which is usually focused on the positive aspects of characters like Jean Grey, rather than inappropriate themes.