She may be able to handle pain alright, or be on some DARN good meds.
I broke my arm, majorly. It required surgery, and wasn't put into a hard cast because my doctor needed to be able to take X-rays every week and access the stitches. I also happen to have an extremely high treshhold for pain. I actually had people in my family who thought I was eggagerating/lying about it, because I just had a brace and bandages for it. And I wasn't acting like I was in any real pain and didn't take any meds for it after the first pill, and I tended to try to use my arm more than I should have. It wasn't until they saw my medical bills (and a copy if the X-ray I got from the doc) come rolling in that they believed me! Lol.
That said, ribs are typically incredibly painful, (I just bruised mine, and it made me move like an old lady for weeks) and tend to limit movement if they are truly broken. To me, it sounds like she may have cracked/bruised them, IF she can handle pain and/or has good drugs... But I would hazard a guess that she probably bumped them good, decided it hurt really bad, and diagnosed herself with broken ones.