You say that in one instance, it took her two months to respond to you, and more recently, you haven't heard from her in about five months. You're getting a message, and you need to face it. She's extremely busy with her current students and the other obligations in her life. When she indicated that she was glad to hear from you originally, and she talked about "staying in touch," those were polite gestures from a person who simply wanted to be courteous, not indications of a desire for constant communication. The smart thing for you to do is back away, retain your good memories of this teacher, and move on. If you continue to send e-mails and try to force contact, you will either continue to be disappointed when responses don't come, or you may push her into having to be blunt and hurt your feelings by telling you that she is busy and doesn't have the time for correspondence with former students. Safeguard your kind thoughts about her by taking the hint and leaving her alone.