I am not saying the brother in law is innocent or guilty. However, there is another angle to this:
-Rebecca has one Instagram account with photos of her as a regular 14 year old under her name Rebecca.Reusch. She has 255 followers. Most likely family, friends and acquaintances.
-She has a second Instagram account with a moniker other than her regular name. The same Instagram account her sister removed photos from. On this account she has almost 36,000 followers. I don't have any adult friends with as much as 1000 followers let alone a 14 year old with 36,000 followers. Imagine the creeps among the 36,000 followers, and it isn't too tough to ascertain her real name on that account if you know your way around Instagram.
Instagram is a marketing tool for your brand when you engage that many followers. She is only 14, has she been looking for fame?
I am linking an article that gives advice how to get your first 1000 followers:
How To Get Your First 1000 Engaged Followers on Instagram
In A nut shell "How to get your first
1,000 followers on Instagram"
3. Look for your audience
5. Post the content interesting to your audience
6. Be consistent
8. Use the right hashtags
10. Post Videos and stories