They aren't. They DO NOT guarantee a mortgage, which is where many, many people get confused. They are based on preliminary applications only. Anything can happen between the issue of a commitment letter and the closing of a deal. No lender will guarantee funding at the beginning of the deal, which is why the letters are useless.
Mortgage brokers are notoriously unscrupulous, and are not even regulated in most states.
If the buyer had thirty days to obtain a mortgage, they can back out with the first decline. They are under no obligation to try to obtain a mortgage from every available lender who will talk to them.
Additionally, if the earnest money was deposited with an out if the buyer was unable to obtain a mortgage, the buyer in this case will get it back. However, in my state earnest money cannot be released until both parties agree to that and sign for its release to a particular party. So, if that is the case in NY, your friend does not have to sign to release it to them until she can speak to an attorney just in case.
IMO, your friend is out of luck. Of course, I do not live in NY, and the laws might be different there.
Thanks....