I've been there a few times. I usually say something like this. "As your friend you have my deepest sympathy and all of my support. I am here for you. Please ask if there is anything you need".

just tell her to stay positive or visit be nice and don't mention it

Offer REAL help. Make a drug store or grocery run for her. Offer to take her out for a meal or a movie. Give her hugs. Give her your phone number and encourage her to call if she needs to talk. Don't scoff at her religious rants - they may give her the courage to face her mortality. Keep it real.

Be there! Having a serious illness can be quite isolating. I agree with most of the comments, doing anything you can do to lighten the load will help. Sometimes just being there helps the most.

From my pov just be there. Unless she broaches the subject there really is no word of wisdom one can give someone who's dying. Just getting them any little thing they want is plenty, e.g. coffee, pie, or just being there. There are tons of great articles out there too, which I'd no choice but to pay attention to when losing both father in law and husband the same year.

I had to follow each lead. My father in law hated it if he could read sadness on my face, which is hard since I've got no poker face game. But I made him knock off dishes he liked etc and made sure to tell him i loved him every time I saw him before leaving.

Just remember to let them guide you. I think one of the most painful things for my husband was when certain people didn't show up that I know he adored, and those same friends had serious regrets because they were too scared to see him until it was too fucking late. People who are critically ill can feel when people are avoiding them. Checking in on them by phone is fine, maybe they're tired or whatever, read cues, drop by another time, or bring something even if they're sleeping. It matters.

Being there is huge, no deep words of wisdom. This is their journey and no one can know how they feel in that situation plus everyone is different.

I'm sorry about your friends condition.

Thoughts are as effective as prayers. A simple "I'm sorry. How can I help?" works for me.

What counts is what a person does. Illnesses throw complications into life and create needs. The best thing a friend can do is take on as much as possible. Bake a casserole! Silently. To me all the saying are somewhat trite and unnecessary.

As a 5 year leukemia survivor I'll tell you what I am saying to a childhood friend who was just diagnosed with breast cancer. I haven't seen her since high school but we reconnected on FB. I'm here for you. Let me know if I can help with information, referrals. etc. BTW she set up a special site for cancer patients.

"Oh gosh, I am with you on this. What can I do to help?"

Telling her that your thoughts are with her is perfectly reasonable.
If it's feasible, you can always offer to take her to doctor's appointments, or to the store when she needs to shop. Offering your time, even if it's just sitting together and chatting, is far more valuable than anyone's "prayers". Prayer does nothing but make the person offering them feel better. It IS hypocritical and makes it easier for those who say it from feeling like they need to do anything else. I'm very sorry that your friend is ill. It's never easy to watch anyone we care for go through any kind of medical crisis.

I had a similar situation. I told the person I was there for them , whenever they wanted to talk, or needed anything I could help with. I ended up helping her husband with much of her final care. Not easy, but I felt like I walked the walk - more than "thoughts and damn prayers" !

If you're not geographically close enough for that, regular contact also means something ...

You're handling it as well as you can. No words really help. Checking up on her and helping where you can mean much more.

My response would be, "I wish you well and hope for the best outcome to your present health issues".

I too stumble across this issue once in a while. Finger crossing and thoughts just don't seem like enough. I believe it's better to say something rather than nothing. Perhaps just offering condolences and support will do.