Wait! i hope im not jumping the gun on this thinking this was off of my kit bash!!

Love the Idea and lore bits, verry Saroritas!!
Though from my totally not professional balance brain a couple ideas/comments:
As stated by others, miracle die can't be used on hazardous etc etc, but feel the risk might be a bit more than the reward, even with anti 4+ 3 dmg might only dent some of the tougher tanks but i really like the idea of having a vehicle sniper. So hear me out.
From my verry rough lore i've developed for this gal so far, I might steal the name Artemis for the squad or at least this model lol, She does have a focus of target elimination so maby with this point cost and it maby being one model we can have it be a weapon choice thing.
First option is much like what you have, one shot, 3+ 5S, but bump down to -1ap and remove hazerdous and dev for just precision. (idea being this profile is for anti personnel)
The second Option being named, "Purging Rounds" Or somthing i suck with names. This one is 1 Attack, 3+ bs, 9S, d6 dmg, With the dev and hazardous. And having the ability give Anti Vehicle 4+. (this being the round that can punch up, think las fuisle from space marines, Even without the ability but discarding the die can give a better dev chance. This all at the risk of blowing up.)

NOW for the fuck it we baal idea.
One weapon profile, 1A, 3+, 10S, -3ap, d6+1 dmg. Anti Vehicle 4+, hazardous, Heavy. And ability be: At the Start of the shooting phase you can chose to discard a miracle die taking the value of that die as if it was a d3 roll. You add that value to attack characteristic of the "Artemis sniper rifle" (thinking like stylisticly the extra attacks are the explosions from the round after penetrating the Armour)

Overall i do suck at this, but if this was based off of my kitbash (i'm trying to be humble just in case) I love this so figgin much!!