It isn't all about you.
Or about your friendship. Or her ability to be a friend.
It could be all those things, of course, but it also could be things that you haven't considered -- things that frankly a "very good friend" of hers would consider before jumping to the conclusion that "I valued the friendship more than she did."
She could be suffering from depression (especially if she had a child recently). She could find herself overwhelmed with something -- her child, problems in her marriage you know nothing about, health issues you know nothing about, problems with her parents if they're in the picture, financial worries she doesn't want the world to know, anything. You say you've tried for weeks to find out what's wrong, but did you frame that as "Did I do something wrong or anger you" or did you frame it as "Are YOU all right, and is there something I can help with? If you need space I understand and I'll keep in touch for when you are ready to talk"?
See the difference? She may indeed be blowing you off as a friend and therefore unworthy of your friendship. But she also may have troubles she either doesn't want to share (yet?) or troubles she feels would make friends distance themselves from her -- so she is putting the distance there first before they can. Especially if she is depressed, she may feel that "People will just hate me if they get to know the REAL me so I'll cut myself off from them because I'm an awful person." That can happen in depression, or in cases where people are blinded by huge issues like marital problems or even ugly financial problems. People start to feel they must hunker down and hide in case they're "found out" as being less than ideal.
I would always assume, first, that a friend was having issues or was sincerely so busy that keeping up was tough for a while. Don't assume that she's just dropped you because she doesn't value you, personally.
Also, if you were in the habit of very frequent communication with her, is it possible she really is too busy to communicate as often as you prefer?