Akari was Shino's first friend. With that being said, she has a very unhealthy obsession for her from keeping locks of her hair to having entire shrines erected for her. From that obsession also comes a fierce loyalty. Shino would gladly fight for the sake of Akari and would throw herself in harms way without a second thought.
As her Amica, Shino is very respectful towards Shirayuki. She also greatly admires Shirayuki not only for her sword skills and impressive status as school but also her mutual hatred for Aria and knowledge of spying on people (particularly people they love). With that being said, Shino diligently studies under Shirayuki and has even borrowed her equipment to spy on Akari.
She refers to Shirayuki with the honorific "Onee-sama."
Much like Shirayuki, Shino hates Aria because as Akari's Amica she is required to work together often or stay overnight thus limiting the time she can spend with Akari. Though not as direct nor willing to assault her as Shirayuki is, she can often be found slumped over in depression at the mere mention of Aria's name or glaring at her when she shows up.
Initially, Shino despises Urara due to the fact she constantly talks down Akari. Once Urara is beaten by Akari and she becomes obsessed with her, they become rivals for Akari's attention. Most of the time, they operate individually to win Akari - often times bumping heads should they run into each other - however they have been shown to set aside their competitiveness for the sake of Akari. As the series progressed they learned to become more accepting of each other as shown when they plotted together for the pool trip. After Akari became Aria's full time Amica, their friendship has grown to a point where they'd willingly hangout with each other to discuss what to do next with winning Akari from Aria.
It should be noted that they are foils of each other. Shino has red eyes, black hair, and is very humble about her wealth and easily flustered over Akari where as Urara has blue eyes, blonde hair, and boasts her wealth and is aggressive when it comes to Akari.