It may or may not be anything to be concerned about. It certainly is possible that she has been bruised in a fall or injured in some other way.
My other concern though is that sometimes we can see bruising like this in an animal that is having problems with their platelets or their ability to clot blood. Another place to look for clues is inside her mouth - does she have any little purple spots on her gums or tongue?
There are a few possible causes for clotting problems. One of the most common is the result of getting into a rat or mouse poison. Another is a condition where the immune system for some unknown reason starts to destroy the body's platelets.
Ideally the best thing would be to have a vet examine her. If you are suspicious that she may have eaten rat or mouse poison then the vet will treat her for a few weeks with vitamin K to help her ability to clot. The vet will probably want to send away a test to see if she is clotting her blood ok.
If you just noticed the spots today and she seems otherwise happy and eating well, it is probably ok to wait a day or two to see if they go away on their own.
Hope this helps! If you have more questions, just hit reply. I will be in between appointments this afternoon so there may be a delay in my response.