How to save a princess (flower) in distress

Q: Our Tibouchina urvilleana tree appears to be distressed this year. The leaves have been much smaller than usual. The purple flowers seem to be about average size, but not the leaves.
We’ve tried 20-20-20 fertilizer and sulfate of ammonia but to no avail. Any suggestions?
A: Princess Flower is a beautiful flowering shrub or small tree that is native to Brazil. It thrives in zones 9-10 but will die back to the ground in zone 8 due to frost.
It needs acid, so adding peat moss to the soil c