Here is another picture with a better angle. In my opinion it really doesn't look to bad but just curious.
http://i1014.photobucket.com/albums/af261/ANelson524/photo2_zps55136dd3.jpg
It looks okay to me but I would keep an eye on it and if there is increased redness or excessive tearing give your vet a call.
I wouldn't worry too much. I would just keep an eye on it and if it seems to get worse, take her in and let the vet have a look.
She was probably rough housing around with your parents' dog and either got scratched or poked. Right now it doesn't look like there's much of anything going on, but good for you for noticing such a small change in your dog's appearance! You are sure to be able to keep her in great shape being so in tune to what is normal for her! You're a great dog mom/dad!
Ghilly
Everything still looks fine, thanks for your help!