.... probably not.... and least not for now.... you may be able to get her to at least go to sleep (like by putting a blanket over her seat like you mentioned), but at this point the nap probably won't be as long or as restful as it would have been in her crib.
truthfully, for now it's probably better to just try & do your errands around her naptimes. (believe me, i know how hard that is) in several more months she won't need as much sleep during the day as you will be able to get out even more. she might even fall asleep in her carseat on the way home & go into her crib without a peep! if worse comes to worst, find a way to go out in the evenings, (maybe when your dh is home or you can get a sitter/friend to watch her) and do your errends then, so at least you can leave the house.