What were the most popular services that the existing business was providing? Is it possible to provide these services outside of an agency?

If your mom knows where the demand was inside that agency then she should draw from that when creating her own company. Perhaps business trips were the main thing they booked? Or young adult tour style trips? If she could focus on what was still selling maybe that is a way to go forward.

Does she still want to be a travel agent or is she looking to do something completely different?