I'm at the one where I have to lvl up to rank 6 one champ of each affinity and amoung them I also have to fully ascend a rank 6 champion. So I have to ascend her or another champ :D

Any advises for my other questions? I really don't know what to do :(

On skill books for Zargala, she takes 15 skill books to complete. I am not saying she is not worth it, but what you are going for is the cooldown reduction, i.e. level 6 on crack armor and levels 6 and 7 on devestate. Getting devestate to 2 turns is what really transform her.

I would not spend your books on her unless you were willing to commit at least a dozen books. If you only have 5 or so books, I would hold them for another champion or until you get more.