Rhetorically speaking; would it be correct for the child of someone who has an identical twin to consider said twin to also be their parent, and any cousins to be half-siblings? Obviously not, because aside from that being objectively weird; people are individuals, not exclusively defined by their genetics, and that extends to familial relationships.
As much as I'd rather they'd have stuck with "Rey From Nowhere", the reality is that Rey's father is Dathan, not Sheev. Sidious is not her father anymore than Shaeeah Lawquane is Omega's step-daughter, because that's not how that works.
Honestly, it's a huge stretch to call Rey his granddaughter at all since 1) Dathan wasn't an exact clone, but a hybrid, and 2) the relationship between Sheev and Dathan was obviously not of the parent/offspring persuasion.
Bo Katan had exactly the right term when she named Jango Boba's "doner", because that seems to be the extent of Sidious's relation to Rey.