Can you also put something (garbage cans, another car, your bike, lawn chairs, etc) in your driveway to block her passage onto the lawn? The lawn I understand is public land, but surely the driveway is personal property... or at least property the home owner gets to decide use of.
And if she complains, etc, I would get all sugary sweet innocent and say "well we had these plans for a while... we tried talking to you but you stormed off in a huff and have been ignoring us, otherwise we would have discussed it with you in advance."