I am trying to join the Peace Corps and I'm trying to gather some references for the application. My last relevant job experience was an unpaid internship I did while working on my degree. My advisor at that internship was always very supportive of me and she said I could use her as a reference in the future if necessary. But that was over 5 years ago and she's probably had 10 more interns since then, I'm not sure whether she even remembers me.

I sent her an email but she never responded, but I think my email may have gotten filtered by the college's email system as this used to be a common issue when trying to email professors from my personal account. I want to call her and ask directly but I don't know how this should be done and what the etiquette is. I've been working at the same place since like a month after I got my degree so it's been about 5 years as well since I've had to apply for anything at all. Is it bad etiquette to ask to use her as a reference after so many years?