OK, from what has been happening to dh I think that I can give you a bit of advice.
Don't look for statistics. In the end they don't 'mean' anything for an individual patient, your MIL could be the 'one' out of the 100 who lives, or indeed the 'one' out of the 100 who dies.
Her long term survival will depend on all sorts of things, and you can't get that info from the 'net. All you will do is upset yourself before the fact.
She needs to know what the staging is. If she has fliud it isn't the best of indicators (dh has this too), but they will still be looking at offereing treatment, if not to cure, then to prolong life and improve the quality of life.
2 months ago dh was dying in front of my eyes, he'd lost 6 stone in about 3-4 weeks, his tummy was distended with 9L of fluid.
Now thanks to good pain relief and chemo, we are planning a holoday in half term, and hoping to take the kids again at easter.
Don't rush into this sweetie, you will deal with whatever happens....you don't have a choice. But your MIL may still have months or years of good life to cope.
Please don't google, you will only upset yourself needlessly. And know one thing, pain and symptoms are controlable, dh is living, thriving proof of this, even though we still know what the final outcome will be, we now have a life to live.