She was made on Earth for Pink Diamond but emerged cracked. She was sentenced to shatter, but managed to escape and hide. That is until an Amber found her. She patched up her cracked gem so the damage would not progress. Amber joked about her no longer being a Cherry Opal for having amber resin in her gem now. So the name Shirley, like a shirley temple, was made for her by Amber.

From then on she followed the Amber around everywhere. She did not form an option of right or wrong, she just wanted to be near Amber. Amber loved messing with humans and shattered many rebels. But Shirley didn't care at the time. Amber was the only one who had accepted her faults.

Amber was very manipulated and went to far with a gem who thought Amber was her friend. She was shattered from the rage of this gem as Shirley watched from afar. The only gem to accept her was gone, she was lost. The gem simple sadly looked at Shirley and gathered the shattered Amber and handed the shards to the shocked and stunned Shirley.
She ran away and went back into hiding with the shards. She crafted them into a pendant to wear around her neck in hopes of finding a way to heal Amber. 

After the war was over. She was abandoned on earth. She luckily was not around when the corruption spread.

For centuries she lived alone in a cave, collecting currupt gems on her own after she was finally able to discover her weapon. She wanted to help as many as could when she got the chance.

She befriended a corrupt Turquoise and kept them around un-bubbled.

She was found be rebels and quickly found how accepting they were. She joined their cause without hesitation.

They helped her realize how manipulative and cruel Amber was to her and others. Although she no longer wants to heal Amber, she refused to take off the necklace.

Her friends and Turquoise were shattered during a battle with a powerful corrupt gem.

Again she was alone. But this time she wandered the planet and continued to collect corrupted gems when she could.

Was in a group known as the Mesa Gems

During Earth's Invasion

She was made in the Kindergarten, therefore had no history before the invasion.
She came out defective with a crack in her gem.
She was deemed trash, until Amber adopted her.
She was unable to use her weapon during the invasion due to lack of willpower, which she needs to harness in order to summon it.
At this time she was terrified of everyone besides Amber
In her mind, Amber was the only one who treated her with kindness.
She  had no real opinion on the invasion due to it being the only thing she  had known, although it had always made her highly uncomfortable.

Post Rebels

By  this time, Amber was gone. She had also managed to find her will power  to summon her weapon around this time. However, due to the invasion  causing her a great deal of anxiety and ptsd, she avoided everyone  besides corrupt gems and other creatures on earth.
She remained in hiding for centuries.
Until the day she had begun to have interactions with others, gems and humans.
This helped her slowly minimize her social anxieties and develop other ways to cope.