“Mama!” Cold Front’s soft, little voice rang out as the filly trotted to her mother’s side. “Are you okay? Do I need to go get Miss Shy?”
 
Rainbow grunted, her hooves scraping the wooden floor in her attempts to stand. “No,” she groaned. “Don’t bother her.” Her voice was weak and scratchy, difficult to listen to. She took a moment to catch the wind that had been knocked out of her when she fell.
 
Coldie’s gaze fell on Rainbow’s wing as the pegasus was able to roll onto her stomach with much difficulty. “Your… wing,” she muttered, her voice dropping to a whisper.
 
Rainbow glanced over her shoulder and unfurled one of the appendages. It was scraggly enough as it was, but Rainbow’s tumble had caused more downy feathers to become dislodged and flutter softly to the floor.
 
“Eh, so what,” she replied flatly. “Not like they see much sky these days, anyway.”
 
Coldie’s red eyes widened. Was she hearing correctly? If Rainbow lost many more feathers, she wouldn’t be able to fly, and she didn’t even care.
 
Coldie swallowed hard. Her mother’s condition had deteriorated more than she thought. And it was all her fault. If she’d had wings like Rainbow wished she had, maybe she wouldn’t be so sad and tired all the time. Maybe she’d be proud, happy. Maybe she’d be herself, or at least who everypony else seemed to remember her as. Coldie had only ever known her as a grouchy bitter mare with a disappointment for a filly.
 
Tears of guilt pricked at Coldie’s eyes as she began to nudge Rainbow’s front hoof, urging her to stand.
 
“You nuh-need to get uh-up,” she stammered, blinking her tears away. Rainbow pushed her off.
 
“Get your hooves off me, I can do it myself.” Wheezing, Rainbow rose shakily to her hooves and turned, limping off with only a last glare in Cold Front’s direction.
 

 
I know I don’t explain it all that well but-
 
Basically, when Rainbow found out she was pregnant, the other pony was already out of the picture, but she was prepared to raise the lil’ tyke on her own. In fact, she was really excited to have her own little feather bab to teach everything she knew. Every trick, maneuver, flying tip, best wing conditioners to use, everything to help it be the best flyer it could be.
 
For the duration of her pregnancy, she and the other mane 5 (who were having their own foal’s around this time) waited and waited for the big day to come. Rainbow had already prepared a sky-themed nursery in her Cloudsdale home and read every handbook on how to train a budding flyer.
 
And then a little Earth pony was born.
 
Not only could it not fly, but it was white. All white. With red eyes and a sensitivity to sunlight.
 
Soon after Cold Front was born, Rainbow had to start completely over in her preparations, though by that time it was too late. Since Coldie couldn’t stay in Cloudsdale, Fluttershy and Pinkie Pie graciously offered for the two to stay as long as they needed (fast forward a bit, and this is how Coldie and Hanky Panky became friends).
 
Postpartum depression hit Rainbow like a truck, and she turned to alcohol to drown her sorrows instead of revealing her immense dissatisfaction and disappointment to her friends. They’d all hate her for feeling the way she did, she just knew it. What kind of mother feels the way about her kid the way she did about Coldie?
 
Fearing judgment, Rainbow continues to suffer in silence as she stops taking care of herself and her health condition (both physical and mental) declines slowly and drastically, as well as losing her job as a Wonderbolt.
 
As a result, Cold Front grows up with crippling self-esteem problems (Fluttershy acted as a second mother, but she and Pinkie had their hooves full with Hank, and taking their time and attention away from him would’ve made Coldie feel worse), as well an obsession with flight and aeronautics, thinking that if she could find a way to fly without wings, maybe she could give her mother everything she was missing out on.
 
This phase eventually tapered off, however, as she realized it was it simply wasn’t possible. This contributed to her jaded and nihilistic attitude toward life, and even a mild dislike for pegasi out of jealousy.