A few years back (4/5) a friend of mine had told me about this book. The main character was an alien (she didn’t know though) and she was described as plain and a nerd, but as soon as the male lead (alien also) came into the school (high school) she suddenly started to become more attractive. As the story goes on she and the boy start to fall in love, another alien comes along (a lord maybe?) and tries to take them away and kill them. It’s later revealed that she is an alien princess.
Just taking a stab, could it be Starstruck by Brenda Hiatt?
Nerdy astronomy geek Marsha, M to her few friends, has never been anybody special. Orphaned as an infant and reluctantly raised by an overly-strict “aunt,” she’s not even sure who she is. M’s dream of someday escaping tiny Jewel, Indiana and making her mark in the world seems impossibly distant until hot new quarterback Rigel inexplicably befriends her. As Rigel turns his back on fawning cheerleaders to spend time with M, strange things start to happen: her acne clears up, her eyesight improves to the point she can ditch her thick glasses, and when they touch, sparks fly—literally! When M digs for a reason, she discovers deep secrets that will change her formerly humdrum life forever . . . and expose her to perils she never dreamed of. Yes, the middle of nowhere just got a lot more interesting!
Apparently, the opening chapters are on Wattpad, so you can see if this matches your friend's memories. I haven't found anything in the reviews about s third guy, but it's possible.
Search terms of site:goodreads.com nerdy girl learns she's an alien princess