"Now and then" aggression

[chasingtailspet]

I have a one year old dog (so she's still in the 'puppy' stage) who is very playful but she's definitely a 'momma's girl'. My friend brought her 8 week old puppy over and my one year old snapped at the puppy (as in teeth showing/growling). My dog has shown signs of aggression but VERY VERY minimal - if she's startled, etc. It's not a daily occurrence - maybe once every other month? She was fine at the start - smelled the puppy and was so excited and then all of a sudden she had enough and snapped. The puppy was getting close to me so I don't know if my dog was telling the puppy to 'back off' or what??

Has anyone dealt with this before? Is there a way to get my dog to STOP acting this way or is this something she'll have for the rest of her life? She loves meeting four legged friends so I don't know what the heck got into her when this happened. I would like to get my dog into doggie daycare so she can be socialized with the other dogs but I am afraid to now after the way she flipped out. Suggestions!?!