I have reread your last post and think that you, without intending to do so, basically diagnosed her correctly, even though the DX you gave her is not in DSM-IV.

She has lost passion for life.

She had friends - she does not engage with them anymore.
She had a job - she quit the job.
She liked sex - she does not want any sex.
She liked parties - she sits home all day long. She has essentially become a hermit. If she is not depressed, she will be due to lack of sunlight since she does not leave the apartment. That said, loss of interest in activities that used to bring pleasure is a symptom of depression - you do not necessarily need to be mopey. Re-read the DSM on depression and see if she qualifies. Maybe you can impress on her the significance of her dis-engagement from the world and losing all her passion for normal activities.

What does a woman who never leaves the apartment buy online? Clothes? She does not need them. Home decor? Not for a tiny studio. Books? Does she read a lot of books?

Since she seems to have lost all her passion, save for the video game and online shopping, lack of passion for sex seems to be an individual manifestation of a much bigger issue, because what you describe is REALLY unusual - her never leaving the apartment is really unusual. I am afraid that you won't be able to solve the sexual part of the problem in isolation.

Other than by trying substances that have a disinhibiting effect on some people though not all.