I take it that she is a New York resident. New York has put out a guide to individual health insurers: New York Consumer Guide to Health Insurers - Introduction
NY is a guaranteed issue state and community rated. This means that a young person will pay as much for a policy and an older person with a serious illness. http://healthinsuranceinfo.net/getinsured/new-york/
My guess is that the likelihood of an inexpensive option is low.
As far as umbrella medical insurance, I had never heard of it. Intriguing idea.
EDIT: NY, like other guaranteed issue states have a problem with adverse selection keeping costs high in the individual insurance market. Looking at the www.healthinsuranceinfo.net
guide for New York, I wonder if it is possible for her to use that to her advantage. Maybe she could risk waiting to see if she is bumping up on the 350,000 yearly limit (bad accident? Need lots of surgeries?) and then apply for a guaranteed issue plan. You would want to be sure that the effective date of the plan is the application date. There is no waiting period or preexisting condition exclusion if she hasn't had a break in coverage.
Just a thought that possibly could be explored.