If you aren't already, try giving her the good boob first. Every second time switch her over to the sore one after a couple of minutes and then put her back on the good one at the end - but don't let her start a feed on your cracked nipple. And maybe try hand-expressing the sore nipple just to get it flowing before you attach her - that way she will hopefully be less likely to suck too hard as she's trying to start things.
Wiping the ointment off is probably worth doing - the ointments that you can leave on before feeds do actually say on the tube that it's OK to do that, so if this one doesn't mention it then wipe it off to be on the safe side.
hugs
Kate