and aerie cant learn the ones i need, as she has learnt all the ones her rather meagre intelligence will allow.
Her parents should never have pushed her to become a mage, better as a secretary or school dinner lady.....
So how does she unlearn spells from the spellbook so she can learn new ones?
Thanks

Try a potion of intelligence. This will lift her amount of spells she can learn.

Both the Potion of Mind Focusing and Potion of Genius will work for this purpose... Any spells copied to your spellbook while under the effects remains after the potion wears off.