I grew up in the Baltimore/DC area, but I'm too young to know about parks that go back as far as you mentioned. However, there is a website that might be able to give you some help.
www.defunctparks.com has a searchable database of closed parks. A search of "Baltimore" came up with a decent number of possibilities. Perhaps you can make a list of these parks for your grandmother, and she can remember which one she went to, which could help you in your research.
Good luck!
Bigg Jon
*** This post was edited by Jon Byron on 5/14/2001. ***