Girlfriend with autism is struggling with sensory overload, need help

Hello.

My girlfriend was diagnosed with autism in the last few years. She didn't struggle too much other than socially and with her intense focus on her interests, so she is considered high-functioning. But lately, she has been getting sensory overloaded more and more and we both don't know where to begin in calming her down, and she doesn't go to a therapist at the moment.

She recently asked me to help her "make a plan" to try to calm her down when she gets this way, but genuinely I don't know much of what to do for an adult, even after a while of research.

I know she has said she is especially sensitive to temperature change, bright light, and loud sound/too many sounds at once. What can I do for those things? 

Feel free to ask for more info if there's anything I left out that you need. I really want to help her and I hate seeing her so defenseless to her breakdowns, so thank you all for your help in advance.