I hope this is the right place

I have an 18month old who has starting rubbing herself and gyrating on cushions. Is this normal, I dont want her to think its bad but just want her to learn that she doesnt need to do it all the time. If anyone can help i have some questions.

- Is it sexual already ie has she worked out she can get pleasure from it? her breathing changes and she gets hot and sweaty.
- will she grow out of it? I keep thinking the more attention i give her the more likely she is going to continue doing it ie it becomes a game.
- how do i handle it? ignore it completely, i tell her she doesnt need to do it for comfort and its not for doing in public, but i dont want to shame her. She was rubbling a balloon at kindygym today and i kept thinking at least if the balloon burst it may deter her a little.

No other mum is going through this yet in my group so thought I would try here, if anyone has advice I would love to heAR. Thought I would have more time to get my head around this phase of parenting.
Thanks Lis