For some reason, upon completion of the restoration ritual spell, I cannot buy guardian circle from the restoration teacher. Having heard of a bug where you might not be able to buy it if you fast travel or don't go straight to her after the quest, I went to an earlier save and redone the quest. I went straight to her and yet still I can't buy guardian circle. If anyone can help me with this I'd be very grateful.

http://www.uesp.net/wiki/Skyrim:Guardian_Circle#Guardian_Circle

Quote from site above concerning the bug.
"Colette is supposed to sell this spell after http://www.uesp.net/wiki/Skyrim:Restoration_Ritual_Spell has been completed, but it is not always available for sale. To get this spell to appear, once you survive the http://www.uesp.net/wiki/Skyrim:Augur_of_Dunlain summoned ghost attacks and he begins speaking ("You are worthy, the knowledge is yours"), start clicking on him repeatedly. You should hear his dialogue skip. Return to Colette and she will have the spell for sale."

Didn't seem to work...

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Some help, please? Someone?

I to have had this problem on my first character ,in the end I had to load back to a earlier save. My problem was I had the perk Master Restoration Spells Cast At Half The Magic, for some unknown reason having the perk made the spell unavailable. I did a test with Faralda and Destruction magic. I went to Faralda when I didn’t have the perk “Expert Destruction” Faralda had all expert spells for sale, without buying anything from her I exited out of her shop options and opened up my skills I added the perk “Expert Destruction” when entered Faraldas shop options again she no longer had the spells Incinerate & Wall Of Storms for some reason these 2 spells disappeared from the game when I added that perk…I test this over and over making sure it was the perk that was removing them from the shop list…sadly it was…and FYI adding the Master Destruction Perk removed the spell Blizzard “ I also tested that”

How to Fix: All you have to do is buy the spells you want before adding the perk.

I hopes this helps you.