Should I tell someone who stutters not to apologise?

Should I tell someone who stutters not to apologise? Okay, so I have this online friend. I don't know whether she has an officially diagnosed stutter, but whenever she's particularly emotional (or tired) she stutters and trips over her words and she usually apologises during or after every time she does it. I usually tell her that she doesn't have to apologise and I don't mind (because I really honestly don't!). What I'm wondering is, is my telling her not to apologise annoying? I don't stutter myself so I'm not sure if I might actually be making it worse, or if it's rude, what's the general consensus here?