I am working on a story trying to decide if it would be more interesting if rainy feathers was raindrops daughter or little sister.
Also all the times you see rainy feathers in the past it was raindrops as a filly.

Hm. To maximize interest, you probably want to keep it set in the Cartoon Timeline. That also makes having to explain other background ponies less difficult. So... Pull a 'Rarity' and have her parents drop off Rainy Feathers for a few days with her older sister in Ponyville while they go off and do other things? That would be the easiest, and you get to do all the 'Bratty Little Sister' things to RD until the end when she goes home.

"Hi Mom. Hi Dad." Raindrops sat at the railroad depot with a calm smile on her face, a much different expression that either of her parents, who walked in her direction almost hesitantly. Rainy Feathers was being very quiet compared to her normal activity level over the last three days. In fact, she did not say a single word or even move from her spot next to her big sister.

"Hello, Raindrops," said her father, looking between his oldest and youngest daughters with a peculiar quirk to his lips. "I see you found a way to keep our little thunderhead under control."

"That's... cruel," said her mother, scurrying forward, but pausing before removing the nearly furlong of ropes that Rainy Feathers was wrapped in or her gag.

Rainy Feathers had no comment other than to continue her fulminating glare with promises of violence once she was released.