Just calm down, 3 emails in a week is a lot. Shes probably just busy and will get to it when she can. This is a pretty common issue. But in general, its better to get the letters early and use interfolio.
I also did not use mine. I used her for my NIH app and it literally took her more than 4 months to submit it. I gave two months to write with my "deadline", and she went over two months later. Even with auto reminders from NIH and my own in the lab. I ended adding other writers and randomly I get a notification that she submitted -_- I had already found a job lol
Wasn't going to make that mistake twice! Hopefully schools understand.