I have a FWD Sorrento with the same weight limit (my vehicle with AWD would be rated for 5K). Since I've decided that my pop-up doesn't quite do it for me, I've looked at what else is out there. At 5K, there would be plenty of hybrid and even lighweight TT options, but at 3500 there aren't many that can be safely towed. Remember, dry weight is not a realistic weight to go by. GVWR for the trailer is a safer weight to consider when looking at limits. If your friend wants to push it, they could see if the dealer would let them load the hybrid up like they would for a trip and weigh it to get the actual weight (or do so after they buy if they are willing to replace their vehicle if need be). There may be one or two hybrid type campers that would be safe, but most of what I've found are the small (too small if your friend has a family) lightweights like the TAB and the lightest two R-pods. Many pop-ups would be a good option if they are interested in towing, need room for a family, and definitely don't want to replace the vehicle yet.
Oh, and of course, if your friend doesn't realize it, make sure to remind them that all weights within the vehicle need to be considered and subtracted from the tow rating. They have always allowed for a 150lb driver and I think they now allow for a 150lb passenger, but all passenger and cargo weights beyond that need to be subtracted from the tow rating.