She is in a pretty hard situation because eats lots of grains and also doesn't has any quality animal source of protein and fat. This is sure a lose-lose scenario.
I've been a vegetarian for 5 years and I can say that I did more or less ok, not feeling never optimal but at least I could get through life with more or less success, I've even run a 10K race in 35 minuts, a sub 3h Marathon, maintained muscle mass with strength training and had enough energy to work and have social life.
But that being said, I finally made a change into paleo and I think that life its a lot more easier this way. I also struggled with grains, also tested for celiac and got negative, but even like this I was always bloated, feeling like crap, joints hurting almost always and feelings like the ones you describe.
I'll tell you the steps that I was following just before jumping into Paleo. I think you can do pretty well on them, but if you ask me, I think they would allow for a C+ or B- healty level, never A. That's just my view on it, of course, based on my findings over the net and N = 1 experimentation.
Being a vegetarian will encourage grain consumption because of a natural lack of other choices, so if you are not aware of the real issue with grains thats the most dangerous issue to deal with. Stopping grains and refined sugars may come top priority. Legumes are next, I don't see them as evil as grains but still high in phytates and lectins and if she has digestion issues, then you got it..
Not eating meat (I guess for personal beliefs) at least one should try to make eggs a staple, and having plenty of good quality dairy would help a lot as long as it's known that does not trigger any auto-immune response and sensitivities. Rotating cow/goat/sheep dairy will allow for more variety of sources. Seek for grass-fed, low carb (so low lactose).
Not having meat also will encourage sources like soy, tofu, seitan and the likes. I have eaten all this with no more issues than the ones I got from grains and I'm not yet sure if they are as threatening as they say but I guess the answer would be yes. A quality Whey Concentrate or Isolate shake may help but if not exercising very hard then may be is overdoing it. There's need for protein but maybe not that much. Hemp seeds and brewer yeast are high in protein, more or less reliable and may come in help.
Eating LOTS of leafy greens and other fibrous greens is a must. That will provide plenty of nutrients.
Some algae could help with vitamin B12 which is the main concern for micro-nutriets in a vegetarian diet. Also a nice boost with iodine.
Nuts can help a lot bust must be cautious that they are not overeaten and also promote those low in omega 6 fatty acids, the best ones may be macadamia nuts, cashews, chestnuts and some almonds.
Healty fats are needed, if lacking animal sources, then olive oil, avocados, coconut oil, flax oil and the ones of the previous commented nuts are good founding.
Special need to watch out for omega 6 sources in order to keep inflammation low. Omega 6 plus high grain that's the worst possible scenario. This is also why lots of greens should help buffer the issue, at least they are known to fight immflamation pretty well.
Fruit is OK but in moderation, vegetarians we can tend to overeat them in the lack of other sources.
If not willing to add all animal sources and need to decide to include one of the least 'sentient' ones, I'd definitely suggest to look into blue fish and seafood in general.
Beware of coffee and tea since they can take fatigue to the next level and they are usually consumed to counter act this, but in the long term it can get worse.
Moderate exercise should be a must, helps a lot.
