I have had a similar experience - an OSO of mine realised that she really wanted someone to be around pretty much all the time, and that even though she enjoyed the relationship with me, it wasn't "enough". Unfortunately being an LDR it was very difficult to make any adjustments to it without financially bankrupting either her or us, so t5he relationship came to an end, unfortunately.
What you can do about it - talk to her about why she feels that she can't completely "have" you - what would be lacking. Gain an understanding and see if anything is possible.
"Listen, or your tongue will make you deaf." - Native American Proverb