Hmm. I think you are right to be concerned and consider it before deciding. It's possible that luggage, shoes etc. could have picked up the bugs. One important factor is how fast they can actually multiply. If it was not an extended time between the two trips, it's hard to imagine that her house had time to become infested to the extent that they would be transporting a lot of them to the cabin. Which reduces the risk, but perhaps not to zero. Too many variables to know. But it seems to me that the risk is much lower here than if YOU visited the original contaminated house. You're two steps away from that.

I would keep luggage and clothes away from theirs during the visit to avoid any cross contamination, and keep an eye on things when you get home, and not worry too much about it.

You can also do some reading at places like CDC or health departments.

Even if your friend isn't a "carrier", you could easily pick up creepy-crawlies at the cabin from the last guest who stayed there. So, I agree that you should go. Just keep your luggage/clothes away from hers during the visit. When you get home, immediately put everything -- including your suitcase and the clothes you're wearing -- into the dryer. Run it on high for 40 minutes. Any hitchhikers will be eliminated that way.

Yes, you should be concerned and take every possible action to keep from introducing them into your world. If there's a dryer at the cabin I would have them put their clothes in on extra hot for a full cycle. I would also have them take their suitcases back out to their car.

Overkill? You only have to deal with bedbugs once to know it's no walk in the park. It tool us over a month to eradicate bat bugs from a house.

As a pest control operator I see no harm in taking this trip. The source would be the grandmother in this situation (according to your friend). This is good she brought this up and shows that she is honest about the whole situation. The chances of getting bed bugs transferred to your home from this scenario is just as slim as getting them from the cabin. Cabins have a lower traffic rate than most hotels and bring the possibilities of bed bug infestation down also. Either way though I'd always inspect all luggage when leaving new places. Use dryer at the cabin before you leave and dry all clothes (this eradicates all bed bugs within the clothes). Here's an article that can educate you on bed bugs also: http://pestproapp.com/bug-guide/39-bed-bugs. Big thing is to be aware of these things and know how to prevent bed bugs. In your case, I would go and have a good time.