I'm trying to teach a few spells to a priestess in my group. She has Intelligence and Wisdom at 18, and she is already level 10. Even though the manual states that she can learn Detect Invisibilty, the game just says she does not have the required skills... how does this thing work?

Also, the manual doesn't mention that a priest can learn Healing, my priestess already came with Healing lv 1.

Higher level spells of each type are not available to the alternate caster classes (Paladins, Monks, and Priests; Rangers, although listed, cannot cast). You need a Cleric or a Wizard to be able to cast all the spells from their respective schools.

(Some characters do come with out-of-class spells pre-learned [Kiriela, for example].)

Thanks for the info!