Fortune's assists aren't super amazing but they can work well depending on how you want to use them.
H Fiber is generally used as kind of a "get off me" assist or when you want to prevent someone from jumping in at you.
If you plan on eventually taking your head off as fortune, cat slide is an assist that can work for stuff. You can pick it by doing qcf mk. One of the problems with this assist though is that if fortune isnt headless when you call her, she'll just do smk which is kinda a mediocre lockdown but since its a normal you can cancel it to a special if you want to alpha counter to the assist.
Headroll is a pretty wacky assist, its got pretty good invincibility and comes with a projectile, you just gotta spend the next assist calling the head back so you can do it again. It also lets you get fortune headless without needing her to be on point, so you can have a good tag if you want in that case.
down+hp at assist select gives you chp or zoom! if you're headless which isnt an amazing assist either way but you can kinda set things up with a launcher assist like chp.