This woman is an idiot who cannot control a dangerous weapon. She basically has admitted she's allowing a loaded gun to roam the neighborhood. AND she's put it down IN WRITING?!? Can we all say "liability", boys & girls

?
A couple of thoughts...
Call animal control/the police/the sheriff.
Make copies of the note, turn the copies over to the authorities.
Contact ALL the other property owners in your neighborhood to warn them.
Contact a local attorney to see what your legal avenues are.
This woman is being irresponsible and negligent, her behavior is downright criminal. She is not changing HER routine, is she, yet she EXPECTS others to have to change THEIR lives to suit her needs? I'm sorry, but if this happened in my neighborhood, it would be time to scorch the earth and get this dangerous animal somehow legally removed. Do whatever you have to.
Someone
WILL get hurt or even killed if you & your neighbors do not take action.
And a Great Dane being a 'biter' is different in my mind from a small breed being a 'biter'...a Great Dane could take a hand off with one 'bite'. I've been bitten on the hand by a small dog. The bite didn't break the skin, but I felt it was my duty to report the incident to Animal Control. I'm an adult, what if this small dog had gone after a child's face...((shudder)). If this dog does get 'in the system', then if he does do something else, he will at least have a record.
agnes!