I have the same but my son is 7 so i don't bath with him and in the past he's seen the scars on top of my legs which are v faded but has never asked however with new ones (i'm having a bad time too so understand the issue you have with that) I've simply hidden it as in I get changed in a diff room and if he bursts in on me in the bath or something I just put my hands over my legs or turn so he can't see because theirs only so many times i could get away with saying i accidently ran into something! (sounds lame i know but it was only thing I could think of at the time and he accepted that!)
I think yeah you will run out of excuses so its either don't bath with her for a while (which would be a shame) or maybe can you wear shorts or something? are they in a place you could get clothing over?
I know how tough it is and I think you're right this is one of those occasions that bending the truth or hiding it would probably be a better plan.
sorry if thats no help,thats just what i do but you may find a better solution o don't know? take care
