Maybe not. This could have something to do with the 'filming' of the Nanoha movie, which seems to be a film that was made in-universe at some point telling the story of Nanoha's first mission for general audiences on Mid.
That could be Vivio cheering on the girl playing her mother as a child.
To supplement Gearhead's answer: Yuuno can shapeshift into a friggin' ferret. Taking on the shape of one's younger self would seem downright trivial, by comparison.
Doesn't this relate to the recently announced "Gears of Destiny" for the PSP? In that game, Vivio and Einhart end up back in the past having to go up against both of her mothers in their youthful form.
