Hi everybody.
I looked at Mother Myrtle's powers and I am not sure if she can recharge spells "just like that". IMO the key is in the phrase "When you would banish [...] FOR ITS POWER". So, I think, that this power affects only cards which are banished to trigger some specific power. In other words - banishment of spells due to lack of specific skill (either Arcane or Divine)should not trigger Mother Myrtle's power, as this banishment is not a power of the card, but only a side effect.