How do I stop my 21month old hitting me? It's beyond a joke I rarely hit her only like 3 times in her life and she never watches anyone hit each other, she's an only child too

If she can't hit first she throws the object in her hands at me, hits and hits me until she drops on the floor crying, I have started the timeout chair but she seems so young for it and saying No it's not ok to hit is honestly getting me nowhere, I live in a one bedroom apartment so giving her space in her own room isn't possible either as it's an open plan.... HELPPPP PLEASE!!!!