You could also try make it fun. Get two brushes she can do a doll while you brush hers or give her the brush and with your hand over the top get her to brush abit of yours then you do a bit of hers.
Thank you all for your replies and suggestions. I ended up combining a few of them, making it fun with two brushes for her to "help" me and also the detangler from Suave REALLY helps! Thank you everyone!