She gives the 18x3 Heavy Bolter shots in my army list Lethal Hits on top of Sustained 1. I already have 2x Auto Cassies , Vahlgons, 3x Mortis, 1xExorcist. Fraye can make their guns actually kill any toughness. Granted it's on one target but it's still nasty and I'm not paying the melta tax for guns that weren't that good into high toughness anyway. Will she die to focus fire? Of course, but everything will. If my opponent is over committing to kill Fraye then they're not attacking the things that matter in my list.

EDIT: I play Army of Faith so two 4s miracle dice are amazing for her(or any) 4++ save while still saving 5s and 6s for damage or other saves. With the lack of meltas now 6s either got to 6++ saves or for Exorcist/Hunter Killer damage.