You need to use exaggeration to make your point come across.

When the friend complains of that impossible blow to her self-esteem caused by getting only three likes on her new profile picture, while you are not sure of whether you can get enough to eat, exaggerate:

"Oh, I am SO sorry. It must feel horrible. Indeed, nothing, nothing at all can really hurt more than not getting enough likes on your profile picture. I only struggle with getting enough to eat, so I am not familiar with the depth of your despair. But I am truly sorry for you and hope that I can improve things a bit by liking your new profile picture. Is it OK or do you only count likes from guys? I really hope to help you with this!"

If she gets the sarcasm and comes to her senses, she is worth keeping as a friend.

If she continues her pity party, then dismiss her without regrets.