in my past life, i worked for several years for a Long Term Care, Skilled Nursing, and assited living company in the states. there is absolutely NOTHING like that here on the island, HOWEVER, its my suspicion that if she is only in need of assisted living, having her live at home with home care would be a great option. A dear friend of mine on the island is an RN from the states, and is actually looking to do this sort of work (she also does child care and babysitting for tourists). Anyway, there are absolutely options for her daily care.
as for medical facilities, there are a number of clinics on the island, but understand you are NOT going to get the same technology here for her (or yourself for that matter). There are however, a number of really great medical practitioners on the island that can give the basic care.
i do know that a friend has a friend who just left the island due to liver cancer in advanced stages. most people would want to be here to die, but unfortunately, the island and country are not able to provide some things he would need in order to be comfortable in his last days.
not knowing your aunts situation, this is the best advice i can give ya! good luck in your decision