How much do you want to spend really?

tcs did give you two links for a budget folder in his post.

The cheapest on the Dahon side is the Broadwalk. Next in line is the Eco. Both do weigh but if the folder is more for storage in the apartment and she's not lugging it up stairs, than those two are good possibilities. Here's a link to a possible vendor you may want to use that list the specs for both folders.

http://www.thorusa.com/dahon/current/boardwalk1.htm

Be aware though that the cheaper the folder the more it weighs and the less adjustable (in terms of arm reach) it may be.

Another option is to look at your local Craig's list for a gently used folder.

Whatever you decide, try and test ride it or see it in the flesh before you buy. Buying it on line (especially a used one) is tricky at best.