I don't think it should harm her occasionally - in fact when I was trying to
trap Boyfie in his scaredy-cat days I was told by the Cat's Protection
League person to use canned sardines in tomato sauce as bait.  She said
that's what they always use to catch even very timid ferals because they are
hard for a cat to resist.
Did I catch Boyfie with them?   Well, not exactly..  He certainly could not
resist them and went into the trap, but he left part of his backside and
tail outside.  He stretched forward and used his paw to reach over the
treadle to scoop the sardines, little by little.  Any mistake in touching
the treadle would have sent the door down, but plan B leaving his tail in
the way of it closing probably would have meant he'd have been able to turn
and put his paw under the door and lift it.
He ate all the sardines, and reversed out ;-)  I was watching him through
the window, it was most frustrating because I thought he needed vet
treatment at that time.
I don't know about the tomato sauce, so if I want to give him or KFC an
occasional sardine treat, I get them in oil.
Their treats have to be *very* occasional though, otherwise they start to
turn their nose up at their regular food and want treat food at every meal.

Tweed

..  So....before I run out and buy sardines to feed her as a treat once in
awhile, are they okay for cats?  It won't hurt her as an  occassional treat,
will it?
...> Jane

I suspect that the sardines are O.K., but I don't know.  Be sure that there
is no onion in the sauce.

Annie

  My wife - Liz - has always had to fight off cats if trying to eat
sardines or pilchards.