I have a small 14 year old dog (chihuahua/miniature poodle mix). She has grown aggressive over the years and is to the point that she'll randomly attack my other dogs and people if they move near me. When I am not around and my sister watches her, she almost never acts up, which has me confused. My father mentioned that she may be "guarding" me, but I am not sure how to get her to stop. When she starts getting aggressive, I put her in a room by herself for a few minutes, but I don't think this is helping beyond getting her to stop before her next episode. None of the other dogs exhibit this behavior.
Any advice as to what I should do to train this behavior out of her would be greatly appreciated! Currently I am too embarrassed and ashamed by her to have anyone over.