If you are worried about it, post the picture (not just the words as it is a cartoon) under a trigger warning. Only those of us who are trying to help you understand it will open it.

Take a screenshot of the comic, and crop it in paint or something so that we will only see the comic and not any identifying information.

She likely just found it funny. We won't be able to really guess until we see it.

And as you've already jumped right back into thinking that she is interested, and/or unhappy with her relationship...

All this is evidence of is that she did not cut off contact with you when she got into a new relationship - that was you. She has told you sh views you as a friend.

Liking someone's picture means squat - except that they like the picture.