"The word 'veganism' denotes a philosophy and way of living which seeks to end the idea of animals as property and exclude all forms of intentional exploitation of, use of, and cruelty to, animals for food, clothing, research or any other purpose; and by extension, promotes the development and use of animal-free alternatives for the benefit of animals, including people and the environment.
In dietary terms it denotes the practice of dispensing with all products derived wholly or partly from animals."
There is nothing non-vegan about it, so if she wants to do it that is fine. It is her body and her choice of what she does with it. I don't think it is gross especially not if you choose to do it. What is gross is drinking another mothers milk thats come in contact with fecal matter and pus, or eating someone else's flesh or something like that.
Anyone saying it is not vegan needs to revisit the definition and understand what it actually means and stop giving people bad answers based off of poor understandings of definitions that in some cases are wholly wrong. The definition above is the most recent and most correct version taking it's roots back to Donald Watson and the Vegan Society he helped found (but with modern additions and clarifications so as to make it stronger)
Vegan because animals are not property