Honestly, I wish I knew what to say.
That sounds like something one of my close friends would say right about now. but enough about me!
Did something happen in her life that could have made her upset? or sad?
You said you are a close friend, have you tried asking her? A lot of times people assume that they can’t ask things that are actually very easy to find out. I suppose it takes a certain amount of emotional energy (and courage), if you’re willing to invest that.
If you’ve already tried asking, and she’s not comfortable with sharing whatever is bothering her, I can tell you that you shouldn’t push her to tell you what’s wrong. When she feels its ‘time’, she will. (she might need some gentle nudging now and then, trust your instinct when drawing the line between concerned and annoying)
I guess the best thing to do would be to just hang out with her or spent time with her or talk to her and let her know that she’s loved and not alone. Sometimes it’s the little things that matter most, right?