Hi Luca,
I'm sorry, I wish I knew too, but I don't for sure.
My intuition tells me something is unnatural about the photo though.
They clearly were bringing balloons into the room as the woman behind her is blowing up balloons.
And if she doesn't have balloons under there, there is a second issue of the pixelation in the image.
Pixelation is when a section of an image is so magnified that single-colored squares become visible.
This appears to happen somewhat around the neckline and where the sweater meets the T-shirt, although it could just be an issue of it being a low-resolution image.