There could be more to the story where he isn't meeting her needs either. Either way, it's not healthy and they need to talk about it. And that was a mean and unnecessary act that she did. I like the five love languages theory, everyone has their "love language" and their own way of needing love.

I've been in this situation (as the low libido one) and it sucks. I became withdrawn sexually from my partner, and in hindsight I believe it was because he wasn't meeting my needs. I know that he did care for me but it felt like the only time he wanted to spend with me was to have sex or eat or watch tv. We rarely actually did anything together (after the initial honeymoon phase and moving in together) in the relationship unless we were traveling and due to health issues we cut back on travelling. I also have gyne issues so that was another factor in my libido. We had lots of sex at the beginning but we also did quite a lot together as a couple. It felt as though once we moved in together he started doing less and less with me and it was just a rare occasion we'd actually do anything together outside of where we lived. As my needs weren't being met (quality time is my "love language"), my libido just dropped and I never felt like having sex with him. I then felt guilty as he said I wasn't meeting his needs, so I'd try, but my needs were continually not being met. He'd feel hurt being rejected from sex, I'd just feel rejected all the time for my needs as he would very rarely do anything with me. In hindsight I felt guilty and shitty for not meeting his needs but mine were not being met. I did try but he didn't understand my reasoning. The toxicity just snowballed. I tried to explain this to him and he just commented something along the lines of "so I have to bribe you to have sex with me by doing things with you". He has some health issues so he is at home sick a lot but it wouldn't take much just to do the occasional thing of his choice together. I feel as though he can stay awake until 4 am gaming everyday, he should be able to feel well enough to do anything of his choice out of the home with me. I'm not saying he can't have hobbies but taking a half an hour here and there for me isn't asking much. When we had more of a fulfilling relationship I'd want to have sex with him, I didn't have to try to make myself want it. Threads like these drive me nuts because often there is more to the story than "bitch won't have sex with me". Not saying that's what op's case is, but I'd imagine a lot of the time it is like that. Some people are selfish and only consider their needs to be important, it needs to be give and take on both sides. And I could be wrong about this for OP, but either way communication is key for fixing this.

Tldr; you have to look at the whole dynamic of the relationship, people have different needs and both partners need to give and take. Sex is important but a relationship isn't just sex.