This is how umbrella policies are designed to operate. Basically, an umbrella policy sits on top of your other insurance policies such as your homeowners or auto policy.
You are able to get insurance on the vehicle. Most likely, she will still need to be listed on the policy even though she doesn't drive because she owns it.
Coverage & Claims
You are only required to disclose medical conditions that may impair your ability to drive safely, such as a seizure disorder or something similar. If the DMV and your doctor have approved you to drive then you are not required to disclose your medications, just beware that you do not drive while under the influence of any medication that could impair your ability to drive safely.
Car Insurance Costs
Insurance companies generally require any household member of driving age be listed on a policy. Policyholders normally have the option, however, to "exclude" anyone they don't want added to their policy.