20 Months Old hitting...how to Manage?

We do time outs for hitting. With a 20 month old I would suggest having a naughty chair and when she hits get eye level with her, keep it short and simple by saying hitting is a no-no, place her in the chair for 2 mins. At this age I would stay in front of the chair and wait the 2 mins out with them but wouldn't carry on conversations or allow toys. Eventually she will get the idea. It's also normal for her to be going thru this stage. This is when they start testing the boundries so you need to be consistant with whatever you choose to do.

I would use the same tactics as with a baby who bites while nursing.
You take them away from the breast and put them down away from you.
Now, 20 month olds are a little more able to understand the cause and affect. If she hits, she goes in her naughty corner or her crib. She needs to relate her behavior to a consequence that she doesn't like. Mainly, it's being taken away from your attention.
She is old enough to understand that her hitting you hurts and if she does it, she goes to another place to stay there for a bit. She may cry and get mad, but that's a technique for you to run to the rescue. I would be a little slow in doing that.
Little kids don't understand how much they can really hurt people and if they think it's a game....they need to be taught that its not funny. For anyone. Especially them.
I think she'll get the hang of it. She's not too young to be taught to say she's sorry and give hugs and hopefully she won't find it so funny anymore.

Best wishes.

It really is a game at this age. She's not doing anything naughty. It feels futile, but you just have to keep saying "no" or "nice touch" or "gentle." You can try grabbing her hand, touching your cheek with it and saying, "Gentle, gentle. That's right."

It's not easy, but try not to be too mad at her. She's just trying to play with her. It's going to take lots of repetition, but she'll get it.

For hitting or biting with my 1.5 year old, I usually tell him "Ow!" and then tell him "Gentle hands!" and show him how to stroke my face softly. If need be, I remove him from the situation. If he does it again, I tell him 'No _____' and put him in his room (door open) just so he realizes that his behavior is not allowed.

My youngest did that at her age as well, along with biting!. I set up the pack n'play in his room and use that as his time out. I didn't want him to have a negative association with his crib. I used short words such as "no hit!", removed him immediately from the situation, and put him in his time out spot for 1 1/2-2 minutes. He would cry at first, then would stop by the time his time was up. I got down on my knees in front of him and gently pointed to his hand and told him "no hit, give love" and asked him to say he is sorry then hug me or his brother (whomever he offended). This has worked wonderfully for us. I think no matter what technique you use, the key is consistency from all caregivers. Nothing will work if you and dad are not on the same page. I also agree with the others that her time out needs to be in a place where she cannot see other household members. We still use the pack n'play for my son's time out. Now that he is 2, he stays in trouble for saying "No!" and occasionally for hitting.
Good luck! This too shall pass!

1 minute time out but I would use a spot other than the crib so there's no association with being bad and the crib.