I took a look at her best Oregorger parse since it's a really good MW fight.
This sounds kind of strange but it just doesn't seem like she's using her abilities enough. Adding spirit would help, but she actually didn't really run into severe mana problems on that kill. She used a pot and took a big chug of tea later on in the fight when she got near OOM.
She only had 289 casts in a 6 minute fight, with 89% activity. That is very low for a MW. I usually cast more spells than anyone in my group by a fair margin, and that's something very common for Mistweavers. For example on my Oregorger parse from yesterday I cast 491 times on a kill that was 20 seconds faster. 99.5% activity.
Here are a couple of more specific spell things:
1) There is so much raid damage going out on Oregorger that she should almost always be spreading renewing mists during "downtime." If the boss isn't casting a torrent or a pool, she should be preparing for the next one. I cast Renewing Mists 57 times on my kill last night, she cast it 36 times. Another way to put this is that for 99% of the fight I had a renewing mist out. She only had 95% uptime...it may not sound like a lot, but it means she is letting it sit there with 3 stacks for prolonged periods, which is wasteful and reduces chi generation. This leads to my next point.
2) She doesn't cast nearly enough Uplift. I don't know your tank healing situation, but I suspect she doesn't need to waste so much chi on Enveloping Mist, especially when it's doing over 60% overheal. She only cast 12 Uplifts the whole fight, and it was still her third most effective heal. I cast 41 in yesterday's kill. Overhealing with Uplift on that fight should not be something that she worries about. I spammed the shit out of it and was still only at 30% overheal with it.
3) She probably casts too much RJW. I know Oregorger is a great fight for it, but no matter how much spirit you have, you shouldn't only have 4 fewer RJWs than Uplift. I only cast 14 RJW on my kill. She should focus on the bread and butter of playing MW on a raid damage fight: Renewing Mists and Uplift.
4) She doesn't use Chi Burst enough, she didn't use Life Cocoon once, and she only used one Revival. Chi Burst should be aimed through one clump of players into the other. I stay in ranged for that fight, so I sort of back up a little bit and shoot CB through ranged and into melee after an acid torrent. If she is not being assigned a specific time / target to Life Cocoon, she should just use it at her discretion. On a tank who is about to die, preemptively on a tank soaking the acid torrent, etc. As for Revival, she should be able to use it twice on this fight whether she's been given an assignment or not. I personally use Revival during each roll phase because of its range. We assign our other CDs during the main phases. My two Revivals during roll phase only overhealed for 22%. Hers was over 50%.
5) Use Expel Harm more. She's using Power Strikes I assume since she doesn't have any Chi Brew casts. An Expel Harm with Power Strikes is the most efficient two chi you can generate as a MW. I had 13 casts in my kill (which even sounds low to me!) and she only had 6.
Basically if I were to distill my advice down for this particular fight, I would say two things. First, the bread and butter of MW on a raid damage fight is spreading ReM and spending chi with Uplift. Focus on this...it's efficient and it generates lots of Chi...she should never be sitting on 3 stacks of ReM on any fight, and especially on a fight where the next burst of raid damage is never more than a few seconds away.
Second, THERE IS ALMOST ALWAYS SOMETHING TO CAST AS A MW ON A FIGHT LIKE THIS. Whether it's Expel Harm or ReM or whatever, she can always be generating more Chi and preparing to heal more raid damage on this fight. There is no reason to have 89% activity.
She didn't waste a single chi she generated, which is great. I wasted 5 on my kill, which isn't ideal but also not the end of the world if it's a byproduct of me attempting to go balls to the wall to max out my throughput.