Remove and wash what you can with bleach in the washing machine...and wash/scrub the rest of it down with some type of bleach mixture...or just dont use it!!
I think you can really wash a stroller. Even if it is on the back porch with hot, soapy water that has a few drops of bleach in it and a big brush, you can hardly hurt a stroller, they are made for mud, rain, and poop, so a good cleaning will not do any damage. And in this case, it will do a lot of good.
That's kind of rude, definitely wash it, that should be good!
She didn't really say anything but "here ya go, I don't need it anymore."
Most baby gear come with covers that come off and can be washed, so there is nothing wrong with taking it to get washed. Anyway I hope she did not think you weren't going to wash it you have a new baby that has to go in there. :-)