Gloria is Borealis' very-special-somepony. When she was a filly she was crying on a flower field and then a colt (Borealis) appeared and cheered her up. She immediately fallen in love with him. She was already beautiful as a filly but now as a full grown mare she's simply gorgeous.
See her as a filly:
MLP: FIM belongs to Hasbro and Lauren Faust ©