That still won't prevent her from going to the house. 

I tell them how I have resources to prevent foreclosures, or how I can buy a house that is not getting sold for some reason and ask them to send me those leads.

We did not get involved in Real Estate as soon as we thought, it was especially tough with no network, no family or friends, not to mention immigration challenges preventing my wife from legally working for almost an entire year.Thankfully we persevered and in the end, both my wife and I have landed some lucrative tech sales roles over the 5 years we've been here, beginning in Florida and now settled in New York City (I know, I know, who would pay so much to live here!?).

The other benefits to hard money is that it’s asset based and many lenders will help you verify your deal actually makes sense and helps prevent you from buying a bad deal.

With that said, I may be looking too far ahead but I like to plan as much as possible so that I can avoid slowing down or preventing a process in the future.

Of course life happens and not everyone that "passes" the screening turns out to be a perfect tenant, but as the landlord the risk prevention starts at square one.

Is there anything I can do legally to prevent them from doing so?

A lot of commercial/bank loans come with prepayment penalties to prevent this from happening, but you shouldn't have that with your hard money loan. 

The buyer does their due diligence by ordering the title work, which is done by the title company, who in turn insures that the home’s title is free of clouds or defects such as judgments, liens, bankruptcies, condemnation etc. that would prevent the seller from transferring clear or marketable title to the buyer.

This can only be lifted in matters where it would be necessary for you to sell or refinance i.e. job moving, death if family, divorce, etc. so while appealing from a low interest rate stand point, the program is designed specifically to prevent investor usage.