Hi Kelsey!
I'm not quite sure what you're trying to ask here? By a "counter argument regarding anorexia" do you mean a way to persuade your friend be vegetarian, despite having anorexia?
If so, I have to say please don't. Eating disorders are such complex illnesses - to someone with anorexia, it's not about what they 'want' to eat, or even what they choose to eat for ethical reasons.
Honestly at this point (and some of you will hate me for this) she needs to do whatever her doctor recommends. If that means eating meat, or drinking dairy based supplements, then so be it. If it was her personal struggle, wanting to avoid meat because it was against her morals, then it might be different. But you have no right to impose your morals on her at this time, even though I'm sure you mean well. If this girl is able to recover, she has her whole life ahead of her - to eat what she wants, and to make a difference for the animals.
Best wishes to your friend (and to you too!) xxxxx