I think she used the wrong words.
As you say, she is right superficially, but she shows a fundamental lack of understanding of why self harmers self injure. It's not about a desire to self harm (which is generally what's inferred by 'choice'), it's more about the need that some people naturally feel to respond and cope with their emotions. Non self harmers don't get that 'positive feedback' from such actions, they get the exact opposite feedback so there isn't any driving force/motivation making it even an 'option' for them. The choice part is only the end product of a self harmer's emotional process, it isn't the beginning, it's an emotional endpoint to which I think that some people can pass to without even making a conscious decision about actually self harming or not, which would mean it wasn't completely by choice at all, simply natural progression. So in that case, no.
To try to avoid self harming, many people will put their tools out of sight/reach. Does that also have the effect of adding extra time to consciously reject using them, allowing it to be more of a decision? And is any decision to self harm taken because it can reduce even more damaging alternatives?