Is my friend crazy?

I think anything is possible in Astral Plane. But I haven't heard this "Building a new reality", Maybe she had built her own Astral World according to her needs. Its Good :)

No your friend is not at all crazy. We can build, I have heard somewhere like this.

I would not be so quick to dismiss this as sane. Though that remains to be seen. It is a very serious matter, as if she is not completely sane, often these things can progress into a worse pyscosis. Ive worked with many mentally ill and know if she is not sane this could get worse.
Now, i know people can build their own world in the astral, but i do not believe (correct me if im wrong people) that people can stay in these realms. You always have to return to your body. So when you say, she says she did not return, and that she is still there, that could be cause for alarm.
She may be speaking of this reality, but her perception of it, it don't know, that is something you will have to determine. I would ask her about her reality. Ask her what she sees. What is her astral plane like. What is the color of the sky? trees? who is there? how is she speaking to you if she is not here, but there? and things like that.
she may in fact be completely sane and just speaking of "reality" as in everyone is in their own reailty. But if your good friends, then i wouldn't dismiss it.
Although, if she is not completely sane, there is not much you can do unless she is a danger to herself. Unless she herself goes to seek treatment, but that would require her to acknowledge that her reality may not be real.

good luck

I agree with Calamity. If she is projecting then eventually she should have to return to her physical body, unless she is a being not of this world?  :o

Wow, I have researched this for over a year and never came across this.... I wonder if she is not wording it right... we all face our fears when there... it can be as real as here or more real and free... I wonder if she learned there and applied it to waking life... in other words created a new reality but yet wouldn't have done it without astral travel......  If this is not the case then Calamity has said everything ... depending on what questions you ask you will not know where she stands sanity wise... Good luck , you are such a good friend to be concerned for her..  :)