You must have a very good relationship, to be invited. Here's some advice on what you can do to be supportive when you visit a Person with ALS (PALS).
First, it helps to understand the disease a little bit.
The motor nerves in her brain and brain stem are being destroyed by ALS, so her muscles can't get a signal to contract. Eventually, all voluntary muscles are paralyzed. The sensory nervous system is not affected, so she can still feel everything. There's no cure.
If she's warning you that she's progressed quickly, she's probably in a wheelchair by now, or needing to be fed. Possibly she's in a hospital bed breathing air through a tube. Hopefully, she's got someone to care for her, 24/7, until she dies. People normally last 2-5 years. A few last longer. My wife was dead in 8 months.
She might have made a decision to stay alive as long as possible, using a feeding tube and trache, or she might have decided to let the disease take her before it gets too advanced. Support her choice whatever it is.
The greatest fear of a PALS is that they might eventually become "totally locked in," that is, totally paralyzed from the eyeballs to the toes. In this far advanced case, all muscles become limp and useless, including the eyes, so communication is impossible.
Remember that her mind is probably totally unaffected by the disease. She still has all her cognitive functions and memories. She is still the person she always was, personality and brilliance and all. Just her voluntary muscles won't move. She can still feel things, both physically and emotionally.
Sometimes, a PALS will suffer Frontal Temporal Dementia, where the personality gets a little short-tempered. Be patient. A few get Emotional Lability, where they laugh or cry uncontrollably for no reason. It's not a change in personality, it's just one possible affect of the disease. Take it in stride.
What can you say? Talk to her or just sit quietly with her. She may find it difficult to talk because either the tongue or the lungs are weak. My wife liked for me to massage her gently quite a bit.
How can you help? Actually, it's her caregiver that may need a lot of help. It's a tiring, 24-hour-a-day job. She may need someone to massage swollen legs, scratch where it itches, reposition her arms, legs, and neck in bed. The caregiver might have little time to sleep, so you can help by doing the laundry, washing dishes, and doing chores that are taking up the caregiver's time.
Some PALS just don't want to be seen like this. So for you, it's really a special honor that she's invited you. I suspect that you are both wonderful people. Good luck. --Mike