@getakick That won’t mask it as well I don’t think, since it sounds like she’s already quite scarred up.
To answer, yes you can tattoo over scars. You will have to work with the scars (pattern etc.) in order to mask them, otherwise it’ll still be apparent. It sounds like you already have a pattern of scars covering your arms. For you, I’d suggest something intricate, where the pattern of your scars will become part of the design as opposed to showing through it, which I would see happening if you got a large and bold tattoo.
Good luck stopping. I know it’s hard. Try to get professional help if you can – they might be able to help you think of ways to stop. Also, if you’re old enough to get tattooed now, that might help you stop – you won’t want to mess up the ink.