9 years too late to ask for letter of support? A friend of mine applied to a distinguished professor and he asked for 5 letters of support. So, she reached out to someone she did a significant internship with 9 years ago and he doesn't seem to be responding. He had been helping her out until a few years ago. I thought it was a bit rude after all the hard work she put into the work.

Is she doing something inappropriate?

She has other supervisors from the corporate world. Can she nominate them instead? Would it work?
It's not too long, but the student should attach an unofficial transcript, a photo and perhaps something else that might jog the professor's memory.

One email is not enough.  Wait a month and try again.  Professors get busy and sometimes something slips between the cracks.