Sometimes my words exceed my experience, but I have those "I remember that time" moments from time to time and can really lay down some wisdom. In regard to her tweet, I would ignore it. You have no idea what it was in reference to, and it could be something as simple as a day to day task being complete and she's ready to relax. You stress and you read it in relation to how you feel and take it the wrong way and question it and it could push her away a bit more thinking you are going crazy. Truthfully, I would completely ignore anything she does that does NOT DIRECTLY APPLY TO YOU. Meaning unless she texts your phone, "what do you have planned for the weekend?" ignore her. If she is on facebook and posts pictures or something you can like it and be the friend, maybe make a BASIC, friendly comment if you feel the need, but don't bring up history or relationship at all.
If it was me, I would unfollow her, remove her from facebook, and change her contact name in your phone. That way if she notices and wants to know why, you can have the reason that you don't want to be constantly reminded of her. But you may not want to go that extreme just yet. That effect could be played back into your favor with a simple rebuttle like "I can't be friends with you, feelings are just too strong for the friendzone status" or something cheesy like that, remember cheesy works.
Stay friends, stay outside and open, don't push yourself back to her but don't just become a hermit, sitting at home, writing dark poetry, stalking her facebook and cutting yourself