Why she keeps switching weapons

You have the quarterstaff attack assigned to left click, so it switches to that weapon to perform the attack. Unbind it or move it to a different key

Your melee attack is set to the weapon it can attack with. So it's set to your quarter staff, so when you auto attack with that ability it changes it automatically.

I'm not sure anyone's properly explained it yet.

When you equip 2 of the same weapon you will have a basic attack weapon set 1 and basic weapon set 2.

Make sure you set the correct one to the corresponding button you want to use if you want to use both weapons. (It'll automatically switch to the correct weapon in the slot)

You can also set a specific skill to only use set 1 or 2 depending on your end goal.

you're using a melee attack. one is a quarterstaff for meleeing, the other is a magic staff for spell casting.

oh boy...