They are often called 'summer quilts'. You can use flannel as a batt, or no batt at all, however, if your friend runs her A/C a lot, you might just want to go with warm and natural. It's cotton and it breathes.
This has been discussed before on the board. Here are a couple of links:
http://www.quiltingboard.com/main-f1...t-t124602.html
http://www.quiltingboard.com/main-f1...t-t183598.html