Try the post office for a forwarding address.
Also, try some of the hotel suppliers, and other hotel operators she may have been friendly with. It is a long painstaking process, but, a name here, a city there, a story and eventually you should buildup a background picture which will give you a clue where to look
If you hire a professional, it will be very expensive, and usually they will only handle it as a job; so when the money runs out, they instantly lose interest.
Make an appointment with someone at the police station. If you are straight with them and can get their advice, they can be extremely useful in pointing-you-in-the-right-direction. Take you time and don't damand; say thank you for whatever they may or may not give you.
OS