Make sure she has access to the toilet paper and walk away. If you are there in the room with her or close by she feels she has you to do it. Busy yourself and make yourself unavailable to do it. Let her scream, cry, throw a tantrum, but stand firm and tell her she needs to do it herself. Since rewards sometimes work for potty training, and wiping IS part of being potty trained, maybe set up a little reward for her, say, she wipes on her own without asking/demanding you to do it for the next couple of weeks and you'll take her out for a new something for being a big girl? (It could be a new backpack for school or something she needs.) After doing it on her own the next few weeks it will be a habit, in time for school.
My guy turned 3 in April, potty trained a year ago, and I have had him wiping since he first started using the potty. This was all in preparation for preschool, which he starts in about a month. He needs to be completely potty trained, the adults cannot help him (and I'm glad for that!) He has improved all along the way, honestly he does a great job, he doesn't even want me to help (but I still check) ツ