My daughter keeps sucking on her hair?

My 4 1/2 year old keeps sucking on hair. The problem is, it dries from her saliva and gets matted and so it is a pain (literally and figuratively) to get a brush through her curly hair every day. Every time I see her I tell her to get her hair out of her mouth but literally 30 seconds later it is back in. Every day I explain to her that it wouldn't hurt brushing her hair so much if she stopped sucking on it. How do I get her to stop? I tried putting it back but she just takes the tie out to well, suck on it. She is so obsessive with it the only thing I can compare it to is a kid sucking their thumb. Ideas?