The fact she took the time to write a lengthy text is a good sign. It shows that she was invested.
Also overthinking/overreacting is not good as it only reflects anxiety = lack of confidence. All this does is reinforce the belief that you are not good enough.
Just go with the flow and be the best of you. Just think how your friends/acquaintances/or anyone you know who are not PUAs got their girlfriends.
Do get busy with other chicks in the meantime. Consider them as batting practice so you will be ready for the real game when girl A returns.