You are investing too much in her opinion. It is nice that his family supports you but your emotional wellbeing shouldnt relyon it.
Look, we all get into habits of sending cards or gifts to people we are seeing less and less of until you realise it is silly and stop. There is no malice behind it, you just realise that you are still in the habit of it even though you are no longer close.
If she resented you then why would she have send the previous cards.
And for arguements sake, if she DID blame you, so what? You know you did the right thing and the opinion of someone you no longer see regularly doesnt change that.