Quick Succession Relief on IHT chargeable to grossed up legacy

I am dealing with an estate that is chargeable to IHT.

Prior to her death and due to poor advice, the deceased completed a deed of variation to her late husband’s will in which she redirected legacies stated to be free of IHT exceeding her late husband’s NRB. This resulted in a grossed up legacy for IHT purposes.

I had initially thought that I could apply for Quick Succession Relief as the deceased died within 2 years of her late husband and her estate is now taxable. However, I believe I may be mistaken due to the fact that the IHT was payable on legacies not received by the deceased, albeit the IHT had to be paid from residue.

Any feedback on this would be gratefully received.