This is a fairly recent story, I'd guess not more than five or six years old? It was published online, in English and in an SFF magazine or website, but I'm not sure exactly where or which one. I believe I read it at some point between mid-2016 and May 2017.
The MC is a woman who was, as a little girl, an assassin for a shady governmental or extra-governmental agency. The story starts when she's twelve-ish or so and has, according to some mysterious and never-seen handler, just completed her final assignment - she's offered a card with a near-incomprehensible amount of money on it and basically given carte blanche over the rest of her life.
From there, many years are covered quickly; at first she doesn't know what to do without killing people. She's uncomfortable with no longer being 'invisible' (metaphorically). Eventually she discovers that she loves trying new food, and also that being chubby helps her avoid unwanted attention from men. She combines these interests, spends an absurd amount of money on a camera, and becomes a planet-hopping food blogger. She's still incredibly dangerous - her body is full of deadly cybernetic implants - but people assume she's a spoiled heiress or somesuch and don't pay her undue attention.
Eventually, while traveling, she realizes she's been getting the same unusual dessert at every single restaurant she visits. She confronts a chef at one of the restaurants and threatens his life, and he reveals he was paid to serve it to her. She tracks down the source of the payment, and finds a rich man did it.
The man explains to her (extremely condescendingly, I remember that well), that his daughter is ill, and the only medicine that could save her is super illegal for some reason; however, after seeing the woman's food blog, he was able to hatch a plan to smuggle the individual components needed to make the medicine into the system by using her - he hired chefs to create special desserts with each of the individual ingredients and feed them to her. All the ingredients needed to save the daughter's life are now inside the main character's body.
At first, the MC plans to murder both dad and daughter for tricking her. However, after meeting with the daughter and recognizing a kindred spirit, decides to allow the father's surgical team to extract the substances from her body and save the daughter's life. As the process begins, she reflects that she'll need to contact her handler once more after this - it's implied that the daughter will be taken to be a new child assassin for the shady organization.
Some miscellaneous details:
- The dessert she gets fed is some sort of beautiful bird sculpture that appears to be made of spun sugar. I think the same chef might make it each time?
- The daughter is extremely contemptuous of her father and hates him more than anything. Her sickness is complete agony, and she just wants to be allowed to die already but he won't let her.
- The father does not know anything about assassins or the MC being one.
- A member of the surgical team, however, does - when she gets on the table for the procedure, he notices her implants, realizes what she is, becomes so overwhelmed with fear he's basically incoherent. She has to order him to continue the procedure.
- It's the far future. Planetary travel is definitely a thing, I think interstellar travel might be too.