There are a lot of "hip protectors" out there, but very few of them have been evaluated to determine whether they're actually effective. Of those that have been evaluated, the
results are mixed.
I'd suggest talking to your mother's physician to see whether there's a particular hip protector he recommends. But I should caution you that in a recent survey asking physicians about hip protectors, most weren't familiar with them.
Researchers are continuing to look into the value of hip protectors, but the evaluation process is complicated because they're an unregulated medical device. There's currently an international group that's looking into setting national standards, but until the hip protector marketplace becomes better organized and there's better research on their effectiveness, I think you're better off asking your parent's physician what he thinks.