• Gemming: Smooth (+320 Crit) in yellow sockets, Potent (+80 Int, 160 Crit) in red sockets. Smooth in prismatic / non-matching sockets. Don't match spirit socket bonuses, don't match +60 int bonuses if they have a blue socket.
• Glyphs: Penance and Holy Fire are pretty much the most useful on every fight. The 3rd is interchangeable between Weakened Soul, Inner Sanctum, Fade/Inner Fire (used this for H Thok progression), and Smite (because 10m dps matters)
• From what it seems, the person played disc in T14/earlier. Divine Aegis was a big change to how Disc plays. She seems to be using a little bit too many Power Word: Shields, which is why her spirit is high. It's a mana intensive spell and the more you cast the worse on mana you feel. Lower the shields you cast and you can lower spirit with it. She should be keeping archangel on cooldown almost always.
• Greater Heal < Flash Heal in terms of throughput. Just plain and simple, disc doesn't have haste and the long cast time does not make up the little extra healing that you could get from simply critting.
• Heal and Renew aren't spells for disc. I don't have them on my bar, and the only time I ever did is when I did my proving grounds.
• Thok specifically: Generally this is the "do I know my class?" fight, at least as a healer. Be sure to use Divine Star on CD. You can usually get away with casting PoH in between each screech until about 7-10 stacks, maybe more depending on haste and if you have AMs. Spirit shell before the first screech, but after getting archangel up. Be sure to use inner focus to avoid being kicked. After a certain amount of screeches (it was 8 when I was 10m) I switch to almost completely shield spamming. Roll shields on everyone, but divine star has top priority over every other global.