I can't speak for your gf but I can relate to needing that time alone. Sometimes to just do nothing you know?

It may have little to do with your relationship and more to do with her personal needs.

If things are good when you are together then go with that.

At the risk of offending...my advice is respect her needs and give her the time. Why would her needing alone time "once in a while" make you feel "nervous, restricted, or distant"?