So I was scrolling through the wiki when I noticed in Monet’s gallery that she had a tattoo
I thought nothing of it but then we saw the symbol for the God’s Knights
They aren’t EXACTLY the same but that might be due to Oda’s change in style and it might have been an early version of the GK symbol. In an SBS, Oda said that Monet and Sugar were saved from a “terrible environment”
It doesn’t take a genius to realize that that environment was Mary Geoise. Monet deserted the God’s Knights, was about to be executed, and since Doflamingo is very observant about people’s situations, he saved her (Sugar was also being punished because the Celestial Dragons are assholes)
This means that even in the unlikely scenario that her heart WAS stabbed, she would have regenerated like Gunko, whose upper body (Including her heart) was blown up.