Is Mom's backlash assassination a thing?

Backlash tends to be more useful for getting just enough chip damage in that the enemy caster has to play super conservatively; chip damage also adds up to make other assassinations much more likely. By itself it's not reliable as an assassination. It's an offensive upkeep so will usually be on only one target, and you'll need to damage the jack 16+ times. It's kinda difficult to get that many damaging hits on one target without killing it. Elimination servitors are perfect for this, but there are only 9 of them, they die easily and they want flare as well to reliably hit... Against the black industries example, they contribute 6.4ish hits against a flared slayer; whatever you've got left is likely to kill it too quickly in melee or struggle to break carapace. Forcing the enemy caster to camp and nearly unavoidably getting them down to half hp is great though, and makes sending any battlegroup models forward on the following turn really scary. Good stuff.

I played Iron Mother double Prime Axiom assassination list a decent amount and it is quite fun to play
Typically it takes 3-4 turns before you actually kill their caster. As gobber said you often kill the Warjack before the caster is dead and sometimes they camp a lot. Then you just re-apply it to another Jack and continue the process.

It is very viable to go for since your opponent can't really hide from it and the range is pretty far.
With 2 Axioms you have the best chance to optimize the assassination:
- They have good range on their guns, 2 of which is also 1 point damage like the Elimination Servitors
- They can spawn new Elimination Servitors
- They can still shoot while engaged
- They are fairly resilient (from ranged at least)

With some luck or good dice, it only takes 1-2 turns to do the trick.
If your opponent doesn't have a lot of warjacks, has a beefy caster, or tech to hide the Jacks or avoid it somehow, the game becomes totally different and way more difficult to win.
I don't know if she can do the same trick with the Modulators. In theory yes, but it is way easier to counter than the 2 Axioms - and way less reliable. They can prioritize to kill all your Elimination Servitors and engage some of your Modulators then you are in trouble.
But let us know how it goes!

I paired it with Lucant 2xTEP list.
But Axis 2xTEP would work as well.