As Zipp searches through her family history with no satisfaction, Sunny acknowledges that she knows very little about her own family. This causes a magical scrapbook to emerge from a bookshelf, and as Sunny opens it to see picture of both of her parents, she is pulled inside to relive her lost memories, with Zipp looking through all the pages to eventually bring Sunny back out. Among those memories, we learn that Sunny's mom was just as determined as Argyle (Sunny's dad) to prove that the three pony tribes were once friends and that it would be possible to bring them back together and to bring back magic, but the key difference was that while Argyle was content to stay home and study what he already had, Sunny's mom was eager to go out on an adventure to find such answers. However, Sunny last saw her mom as she left to go on one of those expeditions while gifting her a telescope, and not long after Argyle assured Sunny that her mom would always watch over her "from the stars". After Sunny is finally pulled out of the scrapbook, she uses the telescope she got from her mom to watch the stars.

I just want to say that I used to have the head-canon that Sunny's mom was probably some kind of archeologist who wanted to go out on expeditions to find answers that Argyle couldn't find in ancient documents, so I must admit that I feel quite satisfied to see that I came pretty close to what the true canon turned out to be. It should also be noted that, just like with Argyle, it's never specifically stated what happened to Sunny's mom. It's implied that she had left on an expedition and for mysterious reasons never came back, and while Argyle's assurance to Sunny that her mom would watch her "from the stars" suggests she most likely had passed away before the same thing later happened to Argyle, I'm sure I won't be the only one holding out hope that she's only missing and might be seen again someday (though it sure would have been nice if we got to know the name of Sunny's mother). Not to mention, this episode also give us hope that we might eventually learn more about the missing parents of the other main ponies (keep in mind how many seasons of FiM it took before we eventually got to see the parents of Fluttershy, Rainbow Dash, and Applejack).