I've recently been training restoration up. I now have 85, recently bought a few levels from colette (about 70 - 75) and have returned to buy the last few from her, but there is no longer a speech option to do so.

Does anyone have an idea of how to fix this?

Colette seems to be able to train only up to 75 (expert trainer). However, the dialog option still shouldn't disappear.

Oh well... Am 100 restoration now. I just hope she doesn't glitch after the quest; I want those spells.

Good luck!

And, of course, it screwed up...

The same thing happened to me, but not with just Colette. As soon as I reached the maximum training level for some trainers the option to ask them for training never came up anymore. This definitely happened to me with Aela of the Companions and Grelka in RIften. It only seems to happen to expert trainers. All master trainers still have the dialogue options available even when after having achieved 100 for their respective trainer skill. I've never taken it to be a bug because of this, but I've never gotten training from an adept trainer to test its consistency.

Probably a coincidence. I trained with Arcadia in Whiterun and the dialog option didn't disappear.

No guardian circle for me...
I guess I'll have to build another character for 100+ hours