Do you have any idea how this plan was picked for her? It may be the very best one for her needs. Keep in mind that ALL the plans are based on the prescriptions a person takes. It may be that her prescriptions are so costly that she was put in the Humana $53 premium that covers the GAP. Humana is the only plan that has a tier that will cover that gap if you need it.
If I recall on the Medicare.gov site when you go through putting in all the Prescriptions including the dosage there is a link you can click on where it asks you how you want the various plans to come up. I think there is one that specifically asks if you want the cheapest (This does not necessarily mean premium wise) to come up first. Remember just because you pay $53 a month in Premium in the long run it could still be cheaper because that plan covers the GAP
She has big costs.