Another option is to go to the doctor and ask if you think you should be on antibiotics, for the bite that opened the skin. Go while you are still this bruised. Let them be the bad guy and report it. Around here, doctors report dog bites, just like possible abuse to children gets reported or gun shot wounds. That would take you out of the line of fire at work. I don't know what the laws are down there.
I know that might sound like the coward's way out, but I'm just trying to be sensitive to your situation at work. Trying to get involved with her over this to educate her on what a bad job she's been doing raising her dogs and telling her she needs to shape up could cause conflict, too. Of course you wouldn't express it that way, but that may be what she hears and she could resent it. Think about how much mothers like unsolicited parenting advice. She may have felt bad when it happened, but after the fact, people sometimes have different attitudes. She might prefer to go back to living in denial.
Dogs aren't usually just perfectly nice dogs one day and madly aggressive the next. Aggression is a path of behavior, with signs along the way. Usually the aggression increases as the dog matures and tests it's behaviors, while the owners live in denial. Then it's "suddenly" a problem. I'm just worried about what will happen in the future and who it will happen to.
I'm really sorry this happened to you and that you have to deal with all these issues, that aren't your fault.