Is The Phrase "Clap Her" Correct?

It could be correct, but only in certain contexts.

Usually in modern English the phrase to clap someone means to applaud them - show appreciation by putting the hands together ("Everyone clapped the singer when he finished his song.") So you could have a sentence like this:

"My daughter is performing at the school concert and she's a bit shy - please clap her loudly when she comes on, to encourage her."

The only other use I can think of is ironic. There used to be a phrase "to clap someone in irons" ie to lock them up in metal cuffs or shackles, and from this came a phrase "to clap someone in jail." It's rarely used now, but I suppose you could say "Clap her in jail!" on hearing of a crime that someone has committed. It would sound a bit jokey, though - you probably wouldn't say this if you really meant it.