Shelley Collins is the cousin of Sabrina Collins.
Shelley was previously a stacker at Howdy's but eventually quit and ran a daycare for babies, dogs, and elderly people. Shelley got a dead tooth one day while she was still working at Howdy's where she was hit with a can accidentally by Frank.
Sabrina lived with Shelley for several years before she, Jimmy, and Hope moved into Sabrina's grandmother's house. Shelley was in a masked relationship with Frank online for a long time where they wore masks (hers was a horse and Frank's was a baby).
In the fourth season, during the grocery Olympics, Shelley and Frank figured out that they had been the horse and baby. At the end of the episode, they share a kiss and it is possible that they started dating afterwards.
Shelley is very close with her cousin and the Chance family. One of Shelley's babies that she babysits, Hope Chance, is most likely a very close friend since Shelley was the first name that Hope said. In the third season, during Modern Wedding, Shelley served as Sabrina's maid-of-honor. She also likes to sing and play her guitar a lot.