You raise the question of possible caregiver fraud. The answer to what you can do about it depends on who is paying for the care. If it is the state
or county in which you live, you can contact the adult protective services, or its equivalent in your county and say that you wish to report what appears to be fraud. You need specific information to make any such report: when you last saw the caregiver living or being apart from the elder and what her father does when she is not with him. Dates and times are helpful.
A word of caution: you may not have all the facts about the arrangement. Getting paid for care does not always mean that the caregiver needs to live with the elder. Some programs allow a specific number of paid hours per week for a caregiver. On the other hand, your suspicions may be entirely correct. It is worth reporting your suspicions to the appropriate entity so that an investigation can begin.