Throughout the series Azula avoids mirrors. In the over the shoulder shot of Ty Lee at the circus she isn’t the central focus. When they wipe away the Kiyoshi make up, Azula isn’t in front of a mirror. She doesn’t spend time looking at the water or even fretting over her appearance.
Here’s why:
Azula looks exactly like her mother. When she looks in the mirror she doesn’t see herself. I believe that in the final Mirror Scene Azula’s brain shifts her own reflection to personify Ursa, someone who is a huge source of instability in Azula’s life. Making the part where she destroys the mirror even more symbolic. She’s destroying any hint of her mother, and she’s also simultaneously destroying any shred of sanity left. She’s shattering the old Azula, because after that everything falls apart even more.
Furthermore, in the comics when Azula sees her mother it’s in reflective surfaces. Such as rivers. To me, it seems symbolic, but I could be over analyzing.
Harvest Guardian 