I can see no problem with her using the same hut all the time. But. Is she going to have no contact with any other pigs after the 70Kg is reached? Remember pigs are social animals and need contact with others (or you could get problems with her).
Also if she is going to be using the same hut, i personally would move the hut to clean land with new bedding just before she farrows. That way you reduce the risk of contamination/viruses/diseases to the piglets.