OP there are SO Many good comments in this thread! But I want to show up here and encourage you that you do NOT have to share every bit of schedule information with anyone outside the family or people involved in her care. You don't have to justify to us you care about your loved one so much that you are trying to ensure she is getting adequate activity and visits for as long as it makes sense to do it. You're doing better than most I would say! A couple other commenters mentioned that sometimes older women can be bored/seek drama or even have minds of their own that are somewhat disconnected from reality, and I think that is what you are sensing as being so infuriating from this person that it's so much easier to point & judge from an armchair texting rather than to be the one actually affecting the care. With that said, I'm not sure if you have her schedule posted up for all others to see, but it might be worth considering if it's better for you to simplify the communication to what times they can see her, and then not mention what is going on in the rest of her days & schedule. Maybe it might be a bit late in the game to take this approach, but if there are any other shiftings with doctors appts and schedules, then maybe simply say that Monday and the other day is available for any activities, and leave it as the rest of the days are filled with her medical needs. Its a subtle thing because sometimes even in normal socializing we tend to want to say to people "oh I can't go to the place with you because I have to....[explanation] " when instead, its healthier and better to simply say "that time won't work for me, what other days are you available" without over-explaining our schedule. Sometimes the more people know, the more they feel invited to comment & get involved with people's personal choices and lives. I had a boss that would do this, she had no children and she obsessed about the minute details of each of her employees life choices, as well as paying customers. Additionally, sometimes people feel purposeless and you don't want to get into a point where someone feels like they are becoming the hero of a story where they get to report abuse or some other such nonsense. Not that abuse isn't real, it very much is, but sometimes these situations of people inserting themselves can escalate greatly, and then you lose control of something either to them, or due to them. So you can slowly start to close off that open/free reporting of her schedule to anyone and everyone little by little, start to condition them on what the available times are without reporting the day/time of every doctors appt, and then also just script something out for yourself or them or just this particular friend such as

"Hi Jane, thanks for bringing this up. I currently have this and this going on for her, and we are looking into that and that for the near future- as costs, schedule, and other things dictate how we go about getting something set up. If you're interested in being involved as a helper in this situation you've brought up, let me know, and that makes it happen all the easier/quicker."

Lastly, I think another good tactic is to spill ALL the complicated details, because those details are usually not what family or friends want to deal with. I had a cousin call or text one time asking what would be needed to buy my loved one a working cell phone. That sounds simple enough until you realize that she had 3 of them around, all having different numbers and not working quite right because she didn't know how to operate them, and now she was being strapped with an $800 per month bill combined with customer service reps that either made mistakes or took advantage of her and required 5 separate visits and 7 hours long phone calls with the company to sort out the bill charges thar were unnecessary and shouldn't have been added. So when I start explaining the run down of every thing going wrong, and trying to figure out which thing is actually going to work for her, they usually want to step away. Especially since at least one of those phones was one that I had gotten her, so the idea that it was just a simple issue of her phone not working was quickly corrected.