Dusty is referred to as Dash's 'half-daughter' because while Discord, Flutter's and Dash are married Dusty doesn't share genetic with Dash.
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Dusty Rose, Rainboom and Chaotic Colour had come in from school being followed by Fluttershy. Dash greeted her wife with a kiss, she smiled from the show off affection her feathers ruffeling "Hey, Discord told me you'd been out for nearly an hour, where the kids causing trouble?" the yellow pegasus's ears pinned back as she shook her head no "Not exactly… Some of the colts and fillies were making fun of the triplets when they learned about… Well… About Discords past. Miss Cheerlie wanted me to speak to the class and asked me to come a little before pick-up time. Rain and Chaos took it in stride but Dusty…" her gaze moved to her daughter who was sat on the couch next to angel.
Dash nodded her head in understanding "Want me to talk to her?" Fluttershy nodded her head "I'm gonna make some sandwiches and all of us can go for a picnic." the blue pegasus smiled and nodded her head "Sounds great, dear." she moved across the room approaching Dusty Rose. The hybrid filly was sulking, it made Rainbow Dash frown "Rosey?" the filly turned her head but didn't smile "Heya momma." Dash climbed onto the couch next to the filly "What's eatin' ya." the filly scoffed "The other fillies and colts seem to think I'm gonna eat them." she wanted to be supportive but she ended up laughing, what were the other ponyvillian's teaching their foals "Discord never ate anyone so I think we're safe." Dusty folded her paw and rested her head on them her ears pinning back "But he did magical make everything a nightmare."
Dash nodded "Yeah, he did… Because he didn't know better, no one told him about the magic of friendship. Not until your mom gave him a chance. Even I thought he'd be better turned back to stone." the filly turned her head to face Rainbow "And now you love dad?" the blue pegasus laughed and pulled the filly closer with her wing "Yeah I do. Because your mom convinced me to hear him out and give him a chance. Now look at the three of us, we have mine and Flutter's hoard and we have three beautiful miracles." the fillies gaze flickered away "The other fillies and colts said we're monsters."
Dash shrugged "Fine, then you're our beautiful little monsters. Doesn't matter, you're still all brilliant and kind little fillies. Your mom, dad and I wouldn't change a thing so don't let the other fillies and colts tell you how you should feel about your family… History paints a pretty ugly picture of your dad. But he's not scary or mean anymore is he?" the filly shook her head "And has he ever told you three that you should enchant and change the natural order of thing?" the filly once more shook her head "And we know that's a bad thing right?" the filly nodded her head "See, already off to a better start than your dad had. You know right from wrong and none of you are gonna intentionally do something wrong." Dusty cuddled up to Dash and the blue pegasis noticed her half-daughter smiling "Thanks momma."
Rainbow Dash smiled and used her wing to mess with the fillies mane "Don't mention it squirt. And if the other fillies and colts try and tell you who you are, ignore 'em." she nodded and smiled "I will momma."