I am sorry to hear you are worried about Mimi's leg. My name is Rebecca. I am a veterinarian and will do my best to help.
If she won't put any weight on the leg, she may have a broken toe or bone in her leg, or she may have torn a ligament in her knee. One of the most common reason for a dog to suddenly limp on a back leg is a torn ACL, anterior crucuiate ligament, inside the knee joint.
If she were mine, I would start her on pain medication (if it did not hurt, she would walk on it), gently feel from the toes up to the hip feeling each bone and joint, and possibly take an Xray. If it is just a broken toe, time and pain medication is all she may need. If she has torn an ACL, she may eventually walk on it again but it will always have some pain and arthtitis in it.
Your veterinarian could tell if this is a torn ACL by checking for a "drawer sign" in her knee. Having her checked by your veterinarian would be the best place to start. Until then you might try giving her 1/2 of a low dose or baby aspirin (but no other pain reliever but aspirin, no Tylenol, Advil, ALeve, etc.), once to twice daily, with some food. If she vomits, do not repeat the aspirin.
She damaged something in that leg if she is not putting any weight on it. I would get her checked out as soon as you can. Let me know what other of your questions I can answer, and if this was helpful.