I don't think you're the jerk in this situation. You say you hardly chat with her and that's fine as long as you don't keep pestering her with those.

She's just not over the abrupt change yet so she's giving you the cold shoulder. It's actually hard to "remain friends" even after you've both broken up on good terms. Conversations will seem awkward and just weird because you(or she) isn't used to it. Usually, over time(and a lot of time) you'll both either be able to talk normally again(slim chance, rarely happens) or stop talking altogether (which is usually the case) eventhough both of you promised to "remain friends"