Hi triciamonty,
This sounds deceptively simple, but isn't.
Planning Permission goes with the land, not with the applicant.
However development plans may include specific requirements for applicants.
Permissions granted on foot of such development plans can contain certain restrictions for applicants in relation to the occupation of the house.
Some of these have been questioned colloquially, but not in court AFAIK.
[happy to stand corrected on this, BTW, so speak up anyone who knows more].
Depending on whether your sister was conditioned to live in the house she applied for, for a certain period of time, there could be a planning enforcement issue involved.
Depending on whether or not you built the house per the drawings there may be another type of planning enforcement issue involved.
There may be a way to avoid enforcement by allowing time to elapse, but I'm not sure.
Without knowing more, I cannot say more.
HTH
ONQ
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