Green’s Dictionary of Slang

hot beef n.

also hot meat, ...mutton
[hot adj. (1a) + beef n.1 /meat n. (1)/mutton n.]

a promiscuous woman.

[UK]Farmer & Henley Sl. and Its Analogues III 364/2: Hot Meat (or Beef or Mutton), subs. phr. (venery). – See Bit [i.e. a woman, ‘usu. a prostitute’].