I have friends who have covered scars with tattoos, and they have all found it empowering. Yes, the tattoo can sometimes remind them of the experience that gave them the scar. But they say that it’s more likely to remind them of the feeling they got from reasserting control over their body and turning the scar into something of their choice. There’s no guarantee that you would have the same experience, of course, but it does help a lot of people.
As for the pain, that’s not something I’ve really heard anyone talk about. I texted a few people, and only two got back to me. One said the pain was about the same as any of her other tattoos (maybe slightly more painful), while the other said it was a lot more painful for him. Some quick research suggests that the size of the scar matters, which makes sense because the one who said it was more painful than normal had a big patch of scar tissue on his arm (whereas the other had three lines of scar tissue from cutting herself).
Regardless, you want an experienced tattoo artist for something like this—preferably one who has tattooed over scars before. Not only will they be in a better position to talk about the pain issue, but they are more likely to have the skills required for tattooing scarred skin (which isn’t the same as tattooing normal skin).