MB here.
Just pay her (legally if you're paying her legally for her time now) for the hours. It's the cleanest, best solution.
Offering some level of payment of health insurance costs is a benefit, not payment for work. So if you are otherwise paying her legally I wouldn't do something that isn't in line with your current arrangement.
Reimbursing for health care premiums is not a taxable benefit (or expense) so it can be a great way to offer an additional benefit, or increase in value for the position, without incurring additional costs, but it isn't the same as salary for time worked.
I think the biggest question is where you stand on the legal/ethical issues of compensation. If you're comfortable skirting the rules a bit then you can consider cash or something. If you think it's important to be totally aboveboard then pay her for the time, in line with your existing contract, and document the change to the arrangement accordingly.