What constitutes abuse as pertaining to a restraining order?

You wrote that "we" moved him away from her. Is this "we" siblings? Does someone have POA over your dad? If so, you could arrange to have his social security check direct deposited into his account so there's no tangible check that actually comes in the mail.

If you predict that this woman is going to show up the day the social security check is due you can take the medication out of the house for that day. Remove the booze too. This is not a good long term plan but it would buy you some time to figure out what's going on.

And you need proof. Anyone can accuse anyone of wrongdoing but unless you have proof there's not a lot the authorities can do. Get some proof and then proceed.

Is there some way to keep them apart other than a restraining order? He isn't going to get one against her himself. Do you have POA, is he incompetent? Can you become his representative payee and control his money? I wouldn't go on the route of chasing her for elder abuse. Just try to remove the incentive and opportunity to party with him on his dime and see how much she's around in the future.

Nanny Cam !!! videotape her and give it to the cops. They will do the rest.

Giving prescription drugs to somebody for whom they are not prescribed is criminal. To do so to an elderly person or anyone who does not know better is absolutely abuse. Can you prove it?