Not at that stage though. Like Carole already said, the DEs went after people that were strategically in some way important. She might have been an enemy, she might have had relevant information or skills for one of the two sides... or she was in the way somehow. Voldemort went after Muggleborns in a much more planned way
If her mother was a Muggle-born, though, she could potential have been killed just because she was a Muggle-born. It would have been a fairly well-known fact, and not everyone the Death Eaters went after was an enemy to them (Ollivander, Fortescue).
How exactly is she described as not being very bright? I actually got the impression that she was a fairly intelligent, but shy and insecure girl. In the very least, we have to agree that not a lot is said about her intelligence. And in that case, you can't just say that her running a pub is evidence for her lack of intelligence.
Sorry to say, Hannah isn't described as being very bright, so I doubt her parents were intellectuals (Hannah grew up to be the landlady at the Leaky Cauldron). I could see her from being more from a lower-middle class family where her parents wouldn't have particularily glamorus jobs.