Touching herself

Okay so I was going to google it but that felt weird! My daughter is 18 months now and has started touching her lady bits, I know this is a thing and they get curious but then tonight I was sitting with her and she was on my lap facing me. She laid down to put her head on my shoulder and then started basically grinding her pelvis into me. It surprised me and I was like no stop that! She sat up and laughed! How do I get her not to hump me (lol I still can't believe it happened) but not shame her in doing so?