The problem here is whether that beneficiary is listed as a beneficiary or not. If she disclaims she is no longer a beneficiary and uplifts the other beneficiaries. If she doesnt, she is still a beneficiary. So which does the executor go with?
I would suggest in the absence of a signed disclaimer the executor must list her as a beneficiary with consequent tax issues, if above her threshold. If she subsequently signs or gives her share to another bf, then this is a gift, with further potential tax consequences.