Need a good Fjorm set

It really depends on the units and fodder you have. If you have QR then try to put that on her and if you can try to put on the skill that will give her the most damage to her special. If you are going for arena points, make it aether. Chrom is an easy hero to get as a 4-3 star and allows for a great special. If not things like vantage work too as a B skill.

Vantage or QR combined with her weapon can work, for her proc you could run iceberg with her res stat with quicken pulse to allow a proc hit on her 2nd atk.

I run QR2, Fury3, and iceberg along with her base set