Unexpected worry for dead?

You still knew her and you were in a relationship with her son, so there is a connection whether it was a good one or not. It might help you if you sent a condolence card to your ex. Or, you could also try talking out loud to her 'spirit'. To some people it sounds silly, but it really does provide closure. After my husband's grandmother died (I hated her) I had a 'conversation' with her and finally put my feelings to rest. Give it a try, it's not going to hurt anything, now is it?