[MyPemCharlie]

I would recommend not ever leaving her alone outside without supervision. If she must absolutely be left outside alone for any length of time, you might consider putting a 12x6 foot chain link dog run in your backyard. Above anything, you must make absolutely sure she cannot escape and perform bite #3. You can lose your homeowner's insurance, have to pay for medical treatment, and face heavy civil fines (in Texas it's up to $10,000) in addition to losing Tango.

Is she getting enough exercise and regular daily walks? Often dogs who aren't exercised enough become frustrated, which can result in aggression.

As other's have said, rule out medical problems first. If it's not medical, a good behaviorist should be able to help you manage and keep your girl. Be sure to ask the behaviorist for references and talk to some of their clients before hiring.