@Jodie28 , this is the main problem with trying to treat this yourself. People get confused and lost. It's a bit dicey trying to give advice because when things go wrong, people might blame you.
FWIW, I was one of the ones who "pushed through" and had very good results. Like your mom I respond very well to high-dose b12 (I take injections, too). About a year ago I upped my dosage of methylfolate very, very quickly and very radically. By radical I mean the first time I got sick/crashed after I started taking folate (which happened within 2 weeks of starting), I reacted not by backing off folate supplementation but by increasing it several mg/day until I stabilized at 40mg/day. Then I stayed at that dose for a long time (probably about six months). 40mg/day was how much it took to keep the really bad side effects at bay.
I had a lot of ups and downs doing it this way, though. I got sick/crashed a couple times. Had physical problems and had to constantly tweak dosages of potassium, zinc, salt (for my adrenals), and add in other minerals and supplements as well (like l-carnitine fumarate and the other form of B12, adenosylcobalamin). Sometimes I had to stop some supplements and then re-start them after the side effects calmed down. Some things I used only temporarily to quick fix some acute symptoms. I also worked through a lot of different psychological symptoms (jitteriness, anxiety, anger, processed some old trauma, etc.). It was hard physically and psychologically, plus a lot of work and a lot of reading/research. Also a little pricey. Not an easy road. But after every crash, I always bounced back feeling a little bit better than before.
Currently, about a year after committing to "pushing through" I'm doing very well and back down to a normal folate dosage of about 4mg/day. All dosages of everything are back down to normal levels, and I'm able to get the potassium I need from food. Still taking B12 injections, though. Not as much as your mom, but I love them and hope never to be without them again.
I'm very thankful that I found
@Freddd's protocol and Phoenix Rising. The protocol has been somewhat of a miracle for me. It wasn't the cure-all, and I'm still doing other things in hopes of getting better still, but for sure it's the foundation of health upon which I will build the rest of my life.
So if and ONLY IF you and your mom are committed to the course, AND you are willing to do the reading and work necessary to inform yourself, you might consider keeping on with the folate increase to see where it takes her.
If you decide to do this, please bear in mind that potassium supplementation can be crucial in the process of increasing folate, but too much potassium can also be dangerous, so you would need to educate yourself about that.
And sometimes the sides get to be too much. That's okay. Knowing when to say when, and when not to say when, is half the battle. Goes back to the old adage: Know thyself.
Not sure that's helpful. But it's an alternative view to some others in the thread. I haven't been diagnosed with CFS but I've come to realize after being here for a while and feeling better that I was in pretty bad shape. For example, I had pretty severe PEM for a long time, but didn't know it had a name or that it was a set of symptoms pointing to some dysfunction. I never even discussed it with my doctor because I just thought I was getting old and that it was my lot in life to endure it. I was barely functional (went to work and came home, that was all I could do) but thought that was just how it was going to be for the rest of my life.
I also don't know anything about my genetics or if I have any mutations that caused any of my problems. A lot of people here have some pretty bad mutations that interfere with their ability to make use of B12, folate, and other things. Getting a genetic profile done on your mom might be enlightening. Some people use genetic profile to help guide their supplementation regimen. I never got mine done primarily because of privacy concerns, but also because I'm very comfortable letting my symptoms be my guide to what I take. YMMV. I'm still considering getting genetics done, though, because I think it would be interesting.
Finally, if you've not had very much experience with supplements in the past, or haven't had much experience with how the course of healing can proceed when trying alternative methods, make sure you're prepped for some of the sides and the likely uneven progress you'll experience. Start by searching posts by
@Freddd. Both the sticky threads at the top of this forum are also very good sources of info.
@ahmo has a good document in her signature with the basics of the protocol.
Good luck and good health, whatever you decide.