People. Snape told Moody the bone has to come from the father’s grave. In principle you could buy him a grave (if he doesn’t have one picked out) and have him sit in it while you remove one of his bones. But that might not qualify. You’ll recall that canon!Voldemort killed his father—this would give him a practical reason.
Ignoring the possibility of this occurring in the first place, your objection to her father being alive has rather a large hole:
“The flesh of his servant, willingly given; the blood of his foe, forcibly taken; and the bone of his ancestor, unknowingly bequeathed. Voldemort is a perfectionist...and he would certainly seek the most powerful combination: the flesh of Bellatrix Black, the blood of Harry Potter, and the bone of his father.”
People. Snape told Moody the bone has to come from the father’s grave. In principle you could buy him a grave (if he doesn’t have one picked out) and have him sit in it while you remove one of his bones. But that might not qualify. You’ll recall that canon!Voldemort killed his father—this would give him a practical reason.
This could have been because Voldemort’s father was actually in a grave at the time; the ritual might not always require that.
Ignoring the possibility of this occurring in the first place, your objection to her father being alive has rather a large hole:
She has other ancestors she could use.