I have read all the comments and I think it's impossible to determine meaning without context, which is what I see a lot of people doing here.
If you posted a picture of a painting or quilt, and she responded with "hang that puppy up!", I would interpret her comment as encouragement for you to display your find.
If you simply posted that you had been thrifting and gave no further detail, and her response was "hang that puppy up", I can see how some people would interpret that as her saying you should quit. However, in that instance, I find the phrasing awkward. I've heard people say they were going to "hang it up", as in quit or retire, but I've not heard the word puppy included. Puppy, when not referring to an animal, usually means an object.
Why not simply approach her, explain to her that sometimes things get lost in translation when communicating on social media, and ask her to clarify her meaning.