We were there in July 2008 and I was only 6 weeks out of surgery, so I was very limited in how much and what I could eat; basically my 3 to 4 ounces of protein was it. We only did two buffets: Chef Mickey and Trails End. At both locations I showed the CM the card and was only charged the child's price with no problem. No one seemed to monitor my plate (one salad plate with boiled shrimp, baked chicken, and salmon). At the CS locations I either ordered grilled chicken or the Boca burger, which I understand has now been changed to a true veggie patty that includes rice, which is not allowed until you get to maintenance. Since your DM had surgery such a long time ago, she is probably able to eat most anything, just in limited quantities.
We are returning in June and we just made our ADR's last Friday. We are staying club level at the GF. I will be taking my own deli-sliced turkey and fat-free cottage cheese to have for breakfast while DW and DD enjoy the club breakfast goodies. There is no protein at the club level for breakfast that I have seen. We are using the regular DP and using our TS for dinners. I have already reviewed menus and will pretty much be ordering fish, with no presentation sauce, at each location. My DW and DD will be able to take my dessert back to the room. We have thought about going to Trails End again on our last day for an OOP breakfast and I was planning on using my card then.
Let us know what you find out if you call Disney Dining and if you have any problems in May.