What do you mean "prove that she will not immigrate to the US"??
Clearly, that has been the plan all along, as evidenced by the fact that you tried for a K-1.
Just get married and petition her for a spousal visa. Yes, it will take at least two years. That is just the deal with US immigration at the moment. She's very, very unlikely to get a B visa.
You should really do some research into this process. It is not cheap, easy or quick.