Don't run yourself ragged trying to diagnose her.
My beloved exgf was a lifetime partier/binger - she had periodic kidney stones that would brutalize her. Pyelonephritis comes to mind as well. 'Pain' can mean so many things... I'm no doctor.
And if choublak is right (quite possible) that confounds the whole thing.
I understand. If I heard such news a few months from now I'd be heartbroken.