You were already vulnerable. Anorexia is about control. Being pressured into anything major is likely to trigger disordered eating.

You didn't have full autonomy and control over the choice to abort and you're already under tremendous strain because of the abuse

Of course you'd reach for that coping mechanism. Of course. It's reliable. It stabilizes you; gives you a sense of control over just one thing.

Until it doesn't. Like all addictions, it eventually catches up to you.