My daughter's school recently had a field trip to the Naper Settlement. She's 11. She enjoyed it and learned a lot. Google it to see what there is to do because her class had an arranged tour so it's probably different than what an individual family can do. I was thinking of taking her back with my two younger children this summer. There's a website but I don't have the exact name- sorry.
I've never been to Blackberry Farm so no help there. What about Lamb's Farm in Gurnee? It's a fun and easy outing. There's also Great America and the outlet malls up there but sounds like you're looking for something more educational.
Have fun with your sister.
