How does my grandmother still have an accent?

I'm Italian, a friend of mine came from Australia at age 10 and never lost her heavy (but lovely) English accent.

on the other hand, another friend of mine came from Ukraine at age 10 and speaks now like a native.

but, yes, at 20, that would be too late to shed an accent.

To not speak with an accent, she would have needed to learn English at a very young age. My daughter came to the U.S. at the age of six, she still has an accent.

Some time ago a bartender in Miami asked me what I would like to drink. I answered: "What do you recommend?". She didn't hear it for the music playing too loud. After 2 more attempts I raised my pitch and asked again: "What do you rrrrrrrrecommend?". She said: "Ey, you're German. I like how you guys are rolling your "R"s", The truth is: most Germans don't roll "R"s. In old movies from the 30s however they had to, because old microphones weren't able to pick up the German "R". The most famous ""R-Roller" was Adolf Hiter. That day I gave up speaking without accent. I don't roll "R"s but I speak it the harder, German way. The best of all: You don't have to care about "th"anymore. Its simply "Z". Very comfortable, very funny.

The older you are, the harder it is to lose or change your accent - especially if you don't work at it especially hard.

My inlaws came to the US in the early 80s and still have their accent.

By the time you are in your 20's, your manner of speaking is very much locked in. She will never change.