Well if you were 21 I would suggest having a beer and play a video game that you can relax to. Moments like this are moments that define who you are as a person.
Personally OP I have been in situations like this. I am definitely not a relationship expert and my methods tend to be extreme. My method with relationships is to cut them completely if they don't reciprocate the same feelings because I fully believe in out of sight out of mind. I tend to get too emotionally involved with relationships. I am a very emotional human and I take moments like this personal. I am very hard on myself and I do acknowledge this is my downfall.
So for instance tomorrow I would probably say hi to her and keep our conversations very short by answering questions with one or two word responses or ask questions that are not open ended questions. It probably may seem rude to some people but this is something that works well for me.
I would try my best to avoid her as much as I can. Usually after events like this I tend to start a new hobby/activity. My first hobby/activity was using smokeless tobacco while playing video games. I highly recommend not doing this. If I could go back in time I would had never started. Whenever I play video games now I feel like a need a dip in. Sure during times of video games I feel mentally relaxed and fine with my life but the costs and the affects the dip has not had a good influence on me.
My second hobby/activity was getting involved in a community. I decided to get involved with starcraft. I watch streams everyday and I try my best to interact with streamers themselves and the chat. I also use these live streams to learn more about the game and further improve myself as a starcraft player. My favorite streams are neurostarcraft, wintergaming, livibee, destiny, desrow, TLO, brent, protec, rotti, and nathan. I am currently debating on building a bot, program, that can help streamers out with commands like how nightbot works. I don't know if I will because I personally don't know if it is going to take up a lot of resources. Also, I like to donate to things I like so I have been donating money to these streamers (not all of them at once and I haven't donated yet to some but hope to in the future) and twitch.
My third hobby/activity was developing my overall knowledge of computer parts. I found a wonderful sub reddits like /r/buildapc /r/buildapcsales /r/buildapcforme and so forth. I try my best to help others while learning from others with this hobby. I have built 4 computers so far that I am very proud of. One is a ubuntu server which I currently have team speak server and a email server on! I would have more but I am currently waiting until I get another SSD to make a backup drive just in case my current one crashes. Very exiting stuff.
Another hobby/activity was getting a job (even though this was something that was needed). I worked as a customer service representative for 11 months. I helped out tons of people with emergencies, placing orders, leaving messages for the office, helped people determine if an adapter was suitable for the device they were using, determine if they qualify for the program... etc. It was a great experience but was not the career I wanted. During this time I used the money I got to invest into myself. Bought new clothes, bought a mattress, bought computer parts, got a phone with a plan, bought a snow blower for my mom... etc (all while paying bills). I recently quit because I didn't feel like it was my ideal career path. I would had liked a job that challenged me more mentally.
Hope you get the gist of my hobby/activity examples. There are more but again those are the gist. Basically what I am trying to say is get involved with things you love whether that is sports, computers, fashion...etc, do things that make you happy and also develop yourself as a better human during this event.
I decided to comment to give you my experience/thoughts and to also get this off my chest. Hope all goes well for you OP.