Contacting Professors and Letters of Recommendation
You should absolutely follow up with her. At this point you have no idea why your email did not get answered. She could be at a conference. She could have missed it completely. Or she could have meant to write you back and simply forgot. I'm in my last year of grad school and none of these things are particularly uncommon for professors. Do not waste time wondering about why she did not write you back, simply reach out to her again. Your letter should say something like this: "Hi Professor So and So, I'm following up with you regarding the letter of recommendation for my graduate school applications..." When this has happened to me I almost always get an immediate response with a flood of apologies for the late reply.