Mom is abusive.... and now I look at her differently

So for years now I’ve noticed that after a night of arguing between my mom and my stepdad, that he would have scratches and bruises in different places, even a black eye at one point. My mom would have no bruises or scratches and that made me come to the conclusion that shes just the one doing it. Since then I’ve felt a certain way about it, but tried not to let that make me look at her differently. I recently had a conversation with my dad and he told me about how she would start arguments and fights and end up hitting them, resulting in the both of them fighting each other. After he told me that I just couldn’t look at my mom the same. It scares me a lot to think of her as this person who just hits people and leaves them with bruises like that even though she never hit me and my brothers. Am I wrong for feeling this way? It kinda makes me not like her anymore and not want to be around her and I hate feeling go like this.