I was having some similar problems at work a while back, and went to my t about it. She said that I was taking it too personally, and the managers job is to get the work done. This is a workplace, you've got to keep your emotions out of it.
The managers job is too make sure the team functions, and the work gets done, otherwise they can get fired. So try to look at it from her point of view, if whatever you are doing is disrupting the work flow, it is her job to say something. It's not about you, it's about the work.
It's nothing to be ashamed of if your boss comes to you with concerns, that's open communication, email is not a good way to communicate in this situation. She's not your friend, but the boss.
Just go to work, focus on doing your job, and smile. If she comes to you again, just say ok, can we work together to solve this, instead of taking it so to heart, it's just a job.
When my boss talks to me I just say ok, I'll work on that, or do you have any suggestions on how I could have handled this situation better, those sorts of things, instead of thinking I am worthless, no one is perfect.
Also, if I have to cry, I go in the bathroom, if I am upset I take a walk. I don't let her see the emotions. They don't like that.
Just keep an open mind and look at it from the bosses/companies point of view, they are paying you and have to have things run, or there is no business.