Leotards with hair and nails done perfectly and heavy make up to me equals any number of legitimate sports or occasions.
Now this could be at a
All of which it would totally normal to take a mirror shot and post online. I know I take photos of my kids and post them when they do these things.
No maybe because I live in the tropics but leotards and swimmers are normal clothes everywhere with a pair of shorts/skirt over the top. He'll I did as a teen too.
All totally normal behaviour.
As for 13 years want to seen. Well of course they do its a developmental stage they need to go through to find out who and what they are. That the age where many kids start to firm their teenage identity eg. .. jock, emo. Rocker. Nerd. Good girl/guy. Party girl/guy etc... its all about finding out who you are....