It's good for you to care. I think you should stop initiating sexual activities and loosen up things that are triggering her. I had a similar problem in my teenage/early twenties. It was deeply rooted to my childhood emotional abuse (which caused feeling unworthy, confused about my sexual desires, not fully comfortable with wanting to have sex with my ex partner, not wanting to have sex but having a people pleaser tendencies to perform for my ex partner, insecurities) and fear of being taken advantage of/abandoned. Her hot and cold behaviour is rooted in deep hurt.

I know you don't have intention to use her, but in order to properly resolve this problem you should communicate with her your concerns. Try to initiate a non judgemental and caring conversation about root of this problem, maybe she has some overthinking going on, maybe she was abused, maybe she's lost in her trauma. Show her that you are with her, that you are not going to abandon her, that her feelings and experiences are valid. You are still very young, so it's normal that she needs some adjustments in your intimate life or she might be fearful of intimacy. Ask her if she needs more space or if she needs your help in resolving that, also ask her about that and what could help her feel more safe. Performing degradation kink is mentally safe only if you are sure that both of you are communicating your needs and boundaries effectively.

Tldr She seem unsafe. It doesn't mean you are hurting her in some way, but it points to an issue and she needs to resolve this for her own good. Your partner clearly hides something from you or herself, she can't communicate that or is scared to tell you and it's really affecting her.

Also try to convince her to therapy, maybe couple therapy if it's also about you. Try to be understanding and patient, but only if she's making consistent effort to heal.