This came up during our league night last night.
Both of Rahera’s melee weapons have Blood Boon. Does it trigger separately for each weapon, or is there a solid limit of one Blood Boon per turn, regardless of which weapon triggers it?
I originally ruled only one Blood Boon triggers per turn (matches her old rule from MK3, which was tied to her model and not her weapons). But the current wording isn’t obvious.
I would say that the inclusion of the phrase “…in which it destroyed an enemy model with this weapon,…” it would trigger for each individual weapon.
You got her mk3 rule completely wrong. In mk3 she could trigger it infinite times per activation.
Anyway, RAW she can only use Blood Boon once per activation in mk4. Which might be considered a small downgrade.
But she has two weapons, each of which has the ability. Is there something that you are basing this on?
I took another look at Blood Boon and now retract my comment.
Rules quotes for clarity, because I can’t help myself! 
I concede that this can be parsed two ways, but I won’t delve too deeply into that.
I agree that, because the rule says “with this weapon”, and because she has two weapons with the rule, it can trigger once per activation per weapon.