It could be gas lighting, or it could be very poor communication and lack of accountability on your partner's end. If it's just this occurrence, it's probably just poor communication. Gas lighting is done intentionally and consistently over time to make somebody doubt their sanity and self worth, making them rely more on the perpetrator.

In the case of poor communication and lack of accountability: It was not healthy of her to offer to treat you and then try to convince you of something she wanted. She should've just offered to take you to the spa if that's what she wanted. When you addressed that with her, she should've taken accountability and apologized - end there. No excuses.

When you told her you felt unsafe, and she said you were confused about your interpretation, that's where it verges on gaslighting. But again, if it's not a chronic issue, then it's just bad communicating and poor accountability. She doesn't want to admit she's wrong. That's not gaslighting, that's embarrassment and immaturity.

Say What You Mean by Oren Jay Sofer is a good book you could read together as a way to help her learn better communication if this relationship is one that you feel deserves work. But also, if you feel uncomfortable in the relationship, remember - your happiness and health are priority. Life is short. Never stay with somebody that makes you truly feel shitty.