Have you told her flat out that you don't want to/will not participate in the survey?
I say go ahead & call the cops, if she comes back, and don't explain in detail on the phone when you do.
Don't say 'There's a creepy census worker bugging me'
Just say 'there's a total stranger harassing me at my home, she won't leave altho I've told her repeatedly to go! I don't know her, and I feel very
threatened!' Give your address, then hang up. If 911 calls back (they likely will) do not answer it. A car will be at your drive within moments. Turn the ringer down after you call 911 so you can honestly say "Oh sorry - ringer was off!" when they complain about calling you back & you not answering.
Fight fire with fire...that bitch has no right to infringe on your peaceful existence. Even the gov't wouldn't say that she has. She's just playin' you. Don't let her get away with it again.