M.P.
It is normal for a child this age to throw tantrums but it's not normal for them to try to hurt themselves. I suggest taking her to her pediatrician for an evaluation if handling it by ignoring it doesn't work.
Unless, she only does this after you try to intervene. What happens if you completely ignore her at the start? Your trying to get her to stop may be causing her to increase her angry reaction.
I've found that the most effective way to handle a tantrum with my grandchildren is to go away from them but stay in the same room. I sit on the floor and wait until the screaming and kicking subside and she or he are just sobbing. Once the sobbing lessens I ask if they would like a hug. Usually, they crawled over to me and we rocked. I seldom talked about the cause of the tantrum and I didn't lecture or even suggest that they weren't to do that again.
I just accepted that the tantrum was in response to my saying no or their not being able to do what they wanted which infrequently had nothing to do with anything that I knew about. Once a toddler is overly tired they are easily frustrated. Sometimes, but not often, I've tried to deal with the frustration in a kind way and that put them over the top tantrum wise. It's best to intervene before a child reaches that stage.
But if, after a few of times with you ignoring the tantrum, she still tries to hurt herself, I'd get a medical evaluation. Try staying in the room but not paying attention. Also try leaving the room.
You could also try moving her to a carpeted floor with a large clear space so that she can't hurt herself before ignoring her.
She is having a tantrum because she doesn't know how to handle her strong emotions. A slap on the bottom usually increases a child's anger. I suggest that when a slap on the bottom worked she hadn't gone into a full grown tantrum.
I suggest that you watch for signs of being tired, frustrated, hungry, and try to calmly intervene before she gets this worked up. My grandchildren would and still do respond to my rocking them when I see them looking tired or whining. Quiet time with soft music, a cuddly toy, and soft music in their special corner might help. This is a way of teaching her how to handle her emotions. But you do have to catch them before they start to tantrum.
And I've never seen it help for parents to try to stop the tantrum. The child has to work thru it by themselves. I suggest that the most likely reason for your daughter's extreme rage is her response to your attempt to intervene. But if she doesn't calm down after a few times of you ignoring her, I'd get a medical evaluation.