
The breed mean (average) score is 16, and the Median (most often seen result) is 14. The BVA have only recently started giving the median score on the sheet.
It can be seen from the fact that only 300 Boxers have been scored (we have more of our breed 407 scored than this, and we are a minority breed, where routine scoring has only been done in last 15 years), that few Boxer breeders bother.
From the range achieved 0 to 64 (higher range than in our breed, which has a range of 0-61, mean of 14 and Median of 12), it can be seen that they have nothing to be complacent about and should score all breeding stock routinely to ensure the high scores are not bred from or become more numerous.
As for thye Vet saying the x-ray looks bad. Your sister should have it scored. It may well not be bad at all, as most vets are hopeless at assessing likely hip scores. I know of people being told the plates were not good and result come back with single figure score, and also told they looked good, and they were awful.
Either way your sister needs to know, as if it really is poor then no way should she breed from her bitch.