XD40,
What you did doesn't sound too unreasonable to me. Could argue in the safety of my locked house far away from the situation that you could've should've not drawn, maybe maybe not. Did you call the police after? If not, that'd be the only criticism I'd level. If the gun comes out, or if I think something's going on where I might have to bring it out, I think getting on record with 911 first is very important. In your case, if you don't call the police, you're potentially open to her calling them and claiming you tried to rape/rob/kill her with your gun, and when they come screeching up there you are, a gunman fitting the description. Bad scene which has happened to some people who may have pulled a weapon with some or even total justification, but they got hosed nonetheless.
I worry most about this type of situation in your case, where you're maybe being set up but the bad guys haven't shown enough of his/their cards to necessarily justify drawing and perhaps using deadly force. Maybe it's just someone on drugs, maybe it's harmless, but what if you're about to be violently attacked? As civilians, and in my case without much in the way of hand to hand skills, I'm most vulnerable there in that gray area. I've thought about it, read my state law and a lawyer's advice, and still don't have great answers.
I try to rely on being aware of what's around me, and avoiding possible situations when armed. Don't get me wrong, I'm glad to be able to CCW, but I pay a lot of credence to the people who stress how much a CCWer should always de-escalate, swallow pride, walk away.
I get some wiggle room myself out of how I carry (usually pocket holster with a 357 snubbie or a small 9mm). For instance, once my car broke down at the edge of a not so great neighborhood. Waiting for the tow truck, suddenly in a flash a "rice burner" screeches up behind me where I'm pulled up and a young "ethnic" guy jumps out and starts towards me. I wasn't freaked but I was concerned, and as I'd mentally rehearsed, I backed away from him while facing him, keeping my car between him and me, and put my hand on the pistol grip in my pocket holster. I think he was there to help, but if he'd intended harm, I would've had maybe another second and a half before he'd have been on me. My mode of carry allowed me to be ready to draw quickly, and backpedaling bought me another second or two in case worst came to worst. Also, thinking over it later, maybe he was up to no good. I think my posture and facing him while putting my hand in my pocket like that may have sent a message that may have inhibited him. I don't know from the mental picture I have of your scene whether that would have been feasible or not; for right or for wrong though drawing did back her off.
If I'd had my dog with me as you did, backing away would have been harder, don't want to leave my dog to attack or to get attacked. I'd certainly want to be on my own property rather than off it, to get the most benefit from the law. Not always possible.