In the last ep (or at least I think so...) was Azula's mom really there talking to her? Cause I heard that she was just a hallucination from Azula's mental break down....is it true 或者 not?

No. She was just a figment of Azula's imagination. She was going crazy and thought she saw her mom in the mirror trying to tell her stuff.

It was just a hallucination due to her faltering mental state most likely bought up due to the unfinished bissnus they had. Azula firmly believed her mom hated het even though it's not true.

Hallucination. She disappeared when Azula broke the mirror.