oh my god, it sounds like you are stretched beyond reasonably possible...!
i would go into liferaft mode - and by that i mean get very tough on everything and everyone who is trying to clamber aboard because they sense you are listing a bit!
so,
no to 'just popping in as a friend' - NO WAY NO WAY.! I feel exhausted just THINKING about your situation.
Develop something like Chronic Fatigue Syndrome (sorry to say this, but if you haven't got it already, then you could seriously end up as a candidate as it's a very horrible blend of mental and physical stress things and it TAKES YOU DOWN like nothing else!!!)...but the thing about it is that you HAVE to be 'selfish' with this disease because you can't do anything else.
So develop it swiftish, tell her what the symptoms are (i.e. sudden and totally debilitation, emergency rations of attention for only the totally desperate situation etc etc), and then leave it at that. Get a printout of rules for it off the internet and stick it on th efridge and refer to it whenever she is near - I can't do this, I mustn't do that, etc etc
every time she says 'i want or i need..' point her elsewhere FIRMLY and say that your condition means you cannot even listen because you have no emotions to spare and it woudl upset you too much. give her a hug and the odd bunch of flowers (she sounds like she's got a horrible life).
but NO WAY that you can afford to SINK as there are too many people relying on you that have no options - whereas she does have options.