My 4.5yo girl has discovered it's nice to rub herself onto items like side of the sofa or the top of the climbing frame 
She is aware of what she's doing, does it because it feels nice and she likes it - she says. Gets as far as panting which is so uncomfortable to watch. Apparently does it all the time at nursery (she says), I haven't spoken to the nursery about it yet. Once we've clocked onto what she's doing (which took us a long time to! I thought she was just swinging on the climbing frame that she has in the garden), we've tried ignoring it, distracting her but she gets upset a bit about being stopped. I probably shouldn't have, but told her today if she keeps doing it so much it will hurt and bleed and she'll have to go to hospital. That made her concerned a bit, she hasn't thought about it. I'm worried about uti as well if she keeps doing it.
For context, she's quite mature for a 4 yo and she's bored easily, especially in nursery. She's starting Reception in September and she's been ready for school for a very long time (hence boredom).
Please tell me this is normal. We're freaking out! Do I need to speak to anyone (Gap, health visitors)?? What do I do?????