Your situation sounds very sad. But what do you actually call ‘full blown MS’? For example, is she a wheelchair user? Can she use her arms? See? Speak? Has she got progressive MS or relapsing remitting?
Because there are people on here who have progressive MS who have trouble seeing, hearing, speaking, eating, using arms as well as legs. Who are incontinent, doubly so in many cases. Who have carers help them with pretty much every aspect of personal care.
It’s difficult to address your question without knowing what limits her MS has put on her life.
Can your sister use a keyboard? Even a tablet type? Has she looked at this forum? Perhaps she might?
Regardless of her level of disability, it sounds like she is extremely depressed. Maybe you could encourage her to see her GP and talk about depression?
And what is her personal situation? Does she live with family or independently? And has she a family? And friends? Let us know more about ways in which we might be able to help.