The quest from Moolinda is a life quest but not the main quest line. You need to keep questing through Mooshu until you get the quest to open that dungeon or have a higher level wizard port you in. I helped someone with this same issue last night while I was fishing!
If you got the quest from Moolinda, I assume you are referring to the quest to obtain the Dryad spell. If so, you will simply need to keep questing along the main quest line to unlock the temple. The same thing happens to Storm wizards when level gain occurs faster than the main quest.
The bright side is that you will knock out two objectives in one run of the dungeon rather than having to go back in afterwards to defeat the Plague Oni again.