So I was thinking. Originally she was gonna be based off of platonic love when I realised— Isn't that basically Twilight as Friendship? So I had a better idea: Self-Love.
Frostfall Crystal was born when Flurry Heart was a filly. She's Aromantic Asexual- Meaning she is not able to feel Romantic or Sexual Attraction. Don't get her wrong though, she can still love platonically and aesthetically.
She's the Princess of Balance- Controlling the frozen tundras beyond the magical shield as well as the general weather in the Crystal Empire due to the rarity of Crystal-Pegasi and Crystal-Unicorns.