Oh Jen I just saw this thread! You poor thing and poor Mackenzie! Please don't feel bad, accidents do happen - but when you're a mummy you feel like everything is your fault anyway.

She may have a broken humerus (or separated the top part from the rest), or a dislocated shoulder (which could explain the bruise) or perhaps have given herself a brachial plexus injury (stretched nerves controlling her arm). Either way, it isn't normal and she needs to see a dr today. I hope you get in to a dr and get things sorted out, poor little love. If all else fails as someone said, you could ring the ambulance.

Look after yourself, let us know how you both get on.