Help her by bringing science to the table on her behalf, and with her own experience.
From your friend's perspective, she's been diagnosed with a difficult condition, has no "official" hope for recovery or (possibly) even improvement, and has therefore latched onto even slim hopes for a better future. That's pretty understandable.
Your counterarguments are modestly inconsistent-- you appear to be arguing from a fundamental efficacy position (treatment X produces effect Y in a statistically meaningful proportion on a precisely constituted study population Z), but your actual arguments (as posted here) admit that treatments might work, just for unknown reasons in an unpredictable subset of the population. I can predict which of those your friend is emphasizing more.
Even if her position is only a psychological veil to keep despair at bay, that's not nothing even though it's not a path to a cure or mitigation of symptoms. Further, the placebo effect is a real thing-- a treatment doesn't necessarily need to "work" to make her feel better. If that attitude leads her to reject necessary steps in treating her condition, standing aside might not be feasible. But if she's just spending her time wearing special bracelets or stickers (both real pseudo-scientific "treatments" I've seen), then it may be totally harmless with some upside potential.
Presumably you are not a certified expert in a relevant field (else you wouldn't be defaulting to arguments from basic scientific validity of claims), so what she's primarily hearing from you (regardless of your phrasing or tone) is probably along the lines of:
Your situation is hopeless, your life will never improve, and thinking otherwise proves that you're a fool.
That sucks. It may be what she needs to hear (learning to live with an illness can be hard when you're dreaming all day of an unrealistic, imaginary future in which it's cured), but she's not listening to it right now.
So, what can you do to support her when you obviously don't buy into these science-free schemes? You can help her evaluate these purported treatments.
By that I don't mean "automatically reject them out-of-hand without several published, high-quality studies already existing". But if you've the background knowledge to do so (and if you're presenting yourself as "science only", you should) you can help your friend develop ways to plan, track, and analyze the effects of different alleged "cures". You can suggest something like:
I don't know much specific information about [approach X], so I don't know if or how well it might work. But to help find the most effective option for you, we could draw up a plan for tracking things like how you're feeling, and when it might be time to give up on one treatment or when it's too early to tell if it's working or not. There are a lot of potential options out there, and a methodical approach will help to sift through them.
That might involve drawing up a budget for how much she can spend on these things. There will always be another brand of snake oil, so it's not going to be feasible for her to try them all. But if she has a budget that only allows $200 per month for this, you can be more confident that she won't be spending herself into penury over wild goose chases. She can at least see how spending money on these things fits into her overall financial situation, and appreciate how much she's already spent on do-nothing products and ideas.
If and when she does choose an approach to try, you can help her to evaluate the effects in a more scientific manor. It won't be a double-blind clinical trial, but a sound methodology will help her understand what effect each "cure" has, if any. Possible benefits include knowing when to stop with a specific effort, identify how well promised results match actual results, (possibly) more faith on her part in the scientific method for learning true information, and more.
The best part is that this allows you to not buy into a given "cure" while still accepting the possibility that it will work for her (the methodical approach is how she can be sure for herself and also convince you!). It allows you to be involved and help her throughout her efforts without rendering any judgments in advance (you've laid out what you would consider to be positive and negative results in advance, so the evidence dispassionately either meets or fails to meet the criteria in a fixed period of time). It allows you to bring the best of your philosophical position to your friend in a productive way, rather than just telling her that "science", monolithically, promises that she's doomed.
So you can tell her that you're skeptical of any given idea, but you really want to help her figure out what improvements might be out there. The specifics of how you'd do this sort of observational testing will depend on what each treatment consists of, but even something as simple as keeping a calendar and describing how she's feeling (in terms of her illness) several times per day from a baseline scenario versus over the course of each treatment can be informative, particularly if you're able to operationalize information well (again, specific-situation dependent).
The single, best defense against quackery is a combination of clear definitions of success and failure determined a priori and sound, methodical data. Bringing those to your friend, who may lack them on her own here, can be a great way of supporting her.
For completeness' sake, I will mention that when I've tried this approach (with fad diets, not intractable illnesses), I've not actually had anyone take me up on it-- those people simply weren't interested in tracking that sort of information, for reasons I can only guess. Nonetheless, it did demonstrate my interest in helping rather than judging. It also generally stopped those people from bringing the topic up in conversation, except for the occasional casual mention.