Any advice?

I'm not really sure if this is the right sub for this (feel free to recommend me a more appropriate place to ask this question)

Basically, when she's dealing with a lot of stress, my girlfriend has this really nasty habit/tick where she will use her index fingers to scratch her thumbs, even to the point that it starts bleeding. She just showed me her thumbs and it's probably the worst I've seen up to this point (her thumbs essentially look like they have blisters).

I'm really concerned about this habit, so I'm wondering if there is anything I can do to help her reduce the urge to do this to herself. This isn't some form of self-harm AFAIK, but I'm worried nevertheless.