How to stop hitting?!

My 18 month old will not stop hitting/slapping us! It’s not even when she’s mad, she’ll just do it for fun. I feel like I’ve tried everything. Telling her no, time out, fake crying. It’s just a game to her. No matter what I do she just laughs at me. She’s not a violent kid whatsoever but in the last few months she’s been playfully hitting a lot. It’s starting to become an issue because at play dates she slaps the other kids and is also hitting our dog. I can’t really tell if she just doesn’t understand that what she’s doing is bad or if she is testing us. I wanna believe she doesn’t know any better but I’m not sure. Help!