So, I'm sleep deprived, and the numbers need working out, but hey this is me coming up with some almost drunk ideas.
Starting with Discipline, because I'm an unoriginal bastard:
Power Word: Barrier (Rank 1)
36% base mana cost
1.5 sec cast, 4 minute cooldown (shortened by Aspiration)
Places a protective barrier on the targeted location, absorbing up to 60 000 damage of the members inside. This effect ends if a single target would have lost 50% of its hp before counting any absorption effects. While under Power Word: Barrier, the cost of Power Word: Shield is reduced to zero mana, but cannot trigger effects such as Borrowed Time, Rapture, Reflective Shield, or Body & Soul. Power Word: Barrier lasts for up to 15 seconds, and those affected by it cannot be protected again for 2 minutes.
Next, onto Holy!
32% base mana
Blesses the target with the purity of the Light, increasing the effects of all heal-over-time spells on the target by 10%, and also increases all absorb effects on the target by 5%. In addition, when an attack or spell strikes the target, the attacker receives Blinding Light, reducing their chance to hit with spells and attacks by 3% for 20 seconds. Brilliant Radiance may only be cast on one target at a time (per Priest), and lasts 10 minutes.
Hunters don't really use Scorpid Sting, and last time I looked (things may have changed) Balance druids without mana problems glyph Insect Swarm to drop the miss chance for higher dps, but this fits a Holy Priest wanting to protect those in her care.
Shadow, an old friend returns but it's exclusive to Inner Fire.
19% base mana
Instant Cast, 45 second cooldown
Draws upon the shadow to protect you, increasing your spellpower by <equivalent of next rank of Inner Fire>, your spellhaste by 6%, and has a chance to knock back a physical attacker by 20 yards. This knockback cannot occur more than once every 6 seconds. This spell has three charges.
Also, Improved Inner Fire would improve this spell in both the charges and the spellpower given.