How do i [22M] handel my girlfriend’s [22F] anxieties in a good, positive, and constructive manner?

TL;DR at the bottom.

First a little bit of backstory. We met in 2016 on a boarding school and fell for each other, keeping together even though the relationship eventually became a long-distance one. Doing this time of being together from a distance we met once or twice every month and kept close through chatting and what not. Initially we weren’t sexual, but once we broke through that first barrier of nervousness we couldn’t keeps our hands off each other. We later moved in together, around start 2020.

I’ll be the first to admit, our sex-drives weren’t exactly equal, however they were close enough to where it didn’t create any problems. But once we moved together our sex life slowed down, it wasn’t surprising, after all waiting weeks just to see each other just creats a different sexually tension then living together does.

However it has slowed down significantly in newer times. To the point where sex is a 1/year, maybe twice, thing. I noticed a pattern where sex usually happens when she has peace of mind, again not surprising and also very reasonable. She hasn’t had the easiest of childhood and that has left it marks, so complete peace of mind is a rarity.

Tonight I ask her whether or not she was in the mood, she said no, this developed into a conversation about our sex life. She told me that she feels trapped while we have sex, as if claustrophobia is setting in. She said that she has started to feel anxious about being touched sexually. She said that she feels guilty about rejecting my advances. And she said that she is sorry for being this way. All this while starting to tear up.

If left me with mixed feeling. I’m happy that she has told me, that she trusts me enough to tell me, and that she isn’t losing interest in me. I’m sad that she feels like it her fault and feels the need to apologize about it. And I’m confused as to how I should handle all of this.

How can I help her feel less trapped and less anxious without her feeling guilty about rejecting me?
How do I do it in a way that makes her feelings valid and not like she is the problem?
Is it selfish that i want her “overcome” these feelings just to get a more active sex life?

As far as I’m aware she doesn’t have any history of negative sexual encounters or the like.

TL;DR
My girlfriend of 6 years has confessed to me that she had started to feel anxious about physical touch and trapped while we have sex. This has started after years of a good and healthy sex life.