Hello Helen,
I'm not real positive why someones energy may have disapated like that. BUT, I do know that we are a part of the energy so she could not have lost it.
Being attuned doesn't give the person anything they don't already have. The attunement refines your awareness that reiki is within you. I like to think of a radio station being tuned in so the music comes out clearly.
I like to say this because to say that anyone is given energy that was not their before is like saying that we as the attuners have something they do not. This is duality consiousness that we have to work on so we become stronger and clearer channels for the light flowing within, through and around us. Just knowing this truth is an empowerment in itself. We are One With Creator in all ways, always.
Just like any other practice, reiki when used regularly will clear many channels within us so we flow in different ways. Perhaps your friends energy was really just adjusting or shifting and she didn't feel it like she normally did.
There are so many reason why this could have occured.
I like to think of times when folks say, I feel like I'm not moving forward in my life at all. Then you see them three months later and they tell you that the quiet time they had before was really the beginning of an incredible shift for them, and in retrospect, they see it more of a culmunation of something they were shifting into.
Hope this is helpful,
Love you angel!
Jahnavi