Ideally, I would explain myself, and depending on their response, you can give them a second chance to change the nature of the relationship, or just have further confirmation that you've made the right choice. Not that you need any. You seem fairly confident in your decision and you also did mention this behavior of hers with her before, but I assume she doesn't know how much it's truly impacting the friendship? If so, that's why I think being straightforward and her knowing the extent of how the relationship dynamic affects how you feel about wanting to discontinue the friendship, might get her to reflect or even want to change her behaviour.

From personal experience though, I find it difficult to be forward with issues i have with others in fear of conflict.

Otherwise. You dont owe them an explanation. But it might be the more considerate and harder thing to do.