That's a weird rule! I'd much rather have some dead grass than urine stains all over the sidewalks
Maybe you could carry a bottle of water and "rinse" the pee grass after your baby goes, and show the nosy neighbors that you are conscious of the damage that urine can do to grass and you're diluting the urine to help counteract that.
Stuff like this is the main reason that when we bought our home in 2003, we made sure there was no homeowner's association
The condo commandos are famously ridiculous here!