The second reason is once she owns it, she is responsible for any damage or repairs while that old seller/new tenant are in there. What if the seller damages it moving out or takes all teh light fixtures, it is a hastle that could be avoided. if teh seller stops paying rent and refuses to move out, she is paying a mortgage on a house she cant get intio and has to pay for the eviction.
You would not buy a house sight unseen, so dont buy one you cant see for 304 weeks after you have to close on it. The only way to buy is when you take occupancy immediately after closing.
Check out my blog about this
AFTER CLOSING TIPS AND ADVICE.
Further--though I'm not a lawyer, so this isn't legal advice--if your daughter starts charging rent, then she's de facto established a landlord-tenant relationship with the sellers. And that can give the sellers/tenants a whole bundle of rights and protections.
Your daughter's Realtor is the best one to advise her on what to do. But, really, you want the sellers out of there, not continuing to reside there as tenants.
Hope that helps.