It sucks, but some people really do have trouble falling asleep around others, and then there's also really light sleepers that struggle to stay asleep in the same room as someone else. I've slept in a different room to my husband of 9 years for a long while now, and we both sleep so much better this way. It doesn't mean I love him any less.

I have that issue sometimes. When I have to get up for work in the morning and I'm trying to fall asleep but they're snoring or won't let go of me (arms wrapped around me and I can't move) I find it hard to fall asleep. And I'd rather just sleep on the couch than with him. Some people sleep a little more snuggled than others. Some hate to feel restricted. She didn't do anything wrong by wanting to sleep on the couch. You are probably doing something that's keeping her awake. She could have opted to move back home. Then you'd be even more upset. She still chose to stay at your place, so be happy you have a girlfriend who likes you enough to be with you and to sleep on your couch rather than have her own bed.

It’s very possible. It took me awhile before I could sleep next to my first wife after we got married, because I was not used to sleeping with anyone or anything on my bed except a blanket and pillow. Now it’s not much of an issue, I got used to it, but it took time.

So? Get a second bed. As I said before, normalize the fact that everyone has different sleep needs. It's not less of a relationship if you need to sleep in different beds or even different rooms.

When I started staying at my BF's place I had trouble sleeping next to him as I wasn't used to sharing a bed. I got used to it though.

That CAN be a real thing, and since she's choosing to sleep on the couch I'm tempted to believe that's true. However, you could open a dialogue. Maybe offer things like "we can fall asleep in the same room in separate beds" if she's not good with that THEN ask if it's something to do with you.

It's all about adjustments.

you shouldn't pressure people into uncomfortable situations

So "she claims" something? If she tells you that's how it is for her, why don't you just take her word for it? Is it somehow a dealbreaker if she won't sleep in the same bed with you? She's being honest about her needs and desires. Physician, heal thyself!

I have a hard time sleeping when I share a bed with someone.