Answer

It is possible this is due to a tick carried disease or ingestion of rodent bait leading to a blood coagulation issue.

You can read about bleeding from rodent bait ingestion here

http://www.marvistavet.com/html/body_rat_poison.html

Scroll down on this page to read about autoimmune and tick diseases that can cause internal bleeding leading to bruises along the abdomen

http://www.lowchensaustralia.com/health/imt.htm

If you live where insects are active this time of year fly bites and some other insect bites can cause skin redness too.

Make sure your dog is well by checking her color and her temp if you can.

If your dog might have gotten into anything toxic, appears dehydrated (see if a pinch of skin over the shoulder blade stays stuck in a tent form or flows back down normally when released), has a rectal temp over 103.5F (normal is 100.5-102.5 Fahrenheit or 38 - 39.2 Celsius ), has gums or tongue that look white, blue, gray or yellow tinted where they are normally pink, has a slow color refill if you press on a pink area of gum or tongue, is not breathing well, or is becoming lethargic and non responsive to you as time goes on then you may want to get the dog in to see an emergency vet if one is available in your area.

Also look for bloody nasal discharge, blood in urine or stool, and red spots on gums and tongue or the whites of the eyes as signs of possible internal bleeding.

This site may help you locate an emergency vet if you need one

http://www.vetlocator.com/hotline.php

With luck these are just 'stains' from insect bites but seeing your vet to get her checked for other issues is a good idea.

Hope this helps you!