It's very late in the year to be able to save this hive. Reduced brood causes the remaining brood to be mostly mite infected. What mites are left over (not enough brood for them all) will start attatching themselves to the adult bees. Wing deformity and IAPV will abound in the hive. If I had that situation and I felt the need to attempt to save the hive, I'd try these drastic measures...
Set the hive aside from where it's at, and in it's place, put a broodbox on a screen bottom board.
Go thru the hive, find the frame with the queen on it and set it aside so you know where she's at.
Shake all the bees off all the frames 30 feet or more away from the hivestand with the empty broodbox now on it. As you shake the bees off, put the beeless frames into the empty broodbox.
Only put frames that have honey and pollen stores in them into that box. Do not put any frames of brood in the box, those should be left out of the new setup. If you have enough honey and pollen frames and bees enough to over fill that single box, then add a second box. Keep the most filled frames into the top box.
Also put 2 to 4 frames that are drawn but mostly empty in the center of the bottom box that you have made with the beeless frames.
by now, the box/boxes will have bees that have flown back home. Pick the queen off the frame you have set aside, and drop her into the newly made boxes. She will immediately go down into the combs. Shake her frame clean of bees.
Powder sugar treat the new setup every 4 days for a 12 to 16 days.
The wingless bees will not be able to get back to the new hive setup. All brood will have been removed to remove any new hatching mites (that brood was infected anyways). The hive will be broodless so the powder sugar treatments will have greatest impact of getting rid of any remaining mites. There will be some frames open enough for the queen to lay, if she will this late in the year. Add a full pollen patty to the hive in between the boxes, it will help to enduce laying by the queen.
This is a drastic measure, but is what I myself would try if the hive was strong enough in bees to try to save this late in the year. If the queen will keep laying you'll have better chances of the hive making it. She needs some fresh brood for younger bees to tend to her and to tend to brood and to be the bees still alive in the spring.
Best of luck to your friend.
20+ years, raise my own queens, feed when needed, I treat but have not perfected varroa management yet.