As you all should know, the current era of My Little Pony: Friendship is Magic actually began in Season 5, after the time when Twilight gained her own home castle, which also introduced Starlight Glimmer. At first, she appeared to be friendly to the Mane Six, but in her next three episodes, her villainous nature was revealed. By the season finale, Twilight and her old friends befriended Starlight, and throughout Season 6, taught her about the magic of friendship. Of course, she did have some "untrustworthy" moments during that season, such as befriending Trixie, who we also knew to be a villain in earlier seasons, and a changeling (named Thorax), who appeared to be a former minion of a villain from Season 2 that would later appear in the Season 6 finale, Queen Chrysalis. And avoiding her friendship lessons with Twilight's friends -- that was some disappointment!
Moreover, it was not until To Where and Back Again - Part 1 when Starlight was a temporary "main" character, where she and her "team" rescue the Mane Six and the royal princesses to save Equestria. And now, after her graduation from being Twilight's first student in Celestial Advice, it seems like she's having her own adventures, starting with All Bottled Up and Rock Solid Friendship, the latter where she was NOT confirmed but actually wound up playing a semi-big role in.
We should be aware that we'll pretty likely be in for more Starlight adventures, seeing as though Twilight really needs a break 'cause she's spoken already a record breaking number of words so far since the last two seasons. Only thing still missing that needs to appear in part 2 of Season 7 at this rate is an episode or two where Pinkie Pie has big roles with Fluttershy and/or the CMCs (no more solo Pinkie episodes are recommended), while Applejack, Rainbow Dash, and Rarity all join Twilight in the "Not Needed Anymore Much" club, and all the rest can mostly go to Starlight or somepony else.