There were concerns the child might slip and injure themselves.
Ms Plessis says she took hold of the child's hand and moved them away from the water cooler.
Child A went to another teacher, Jeshika Remsi, who initially claimed she saw Ms Plessis "grabbing and twisting" the youngster's fingers.
The centre bosses were brought in and Ms Plessis was asked to explain herself.
She denied any rough handling, explaining that children often cried if something was taken away from them.
An internal investigation was launched, and the next day Ms Remsi amended her original statement to explain that she had not in fact seen Ms Plessis twist Child A's fingers.
Ms Plessis was suspended and later given a final written warning, which said she would be constantly monitored and supervised "until such time as we feel confident that your handling of children in your care is appropriate at all times".
After returning to work on January 9, 2012, she resigned two days later, saying she felt co-workers were scrutinising her work.
She then took her case to the ERA.
In her decision, ERA member Eleanor Robinson raised concerns that no one actually witnessed the alleged finger-twisting, while other allegations "lacked specificity and were vague in nature".
A fair and reasonable employer would have put more specific claims to Ms Plessis and given her a full opportunity to respond, the ERA found.
The issuing of a final written warning lacked substantive and procedural justification which constituted a breach of duty towards Ms Plessis, the ERA ruled.
Kidicorp's actions meant Ms Plessis was left unable to continue working in her situation, forcing her to resign.
The ERA awarded her $10,000 compensation for "significant hurt and distress".
"It is clear from her letter of resignation that this had been a job which she had greatly valued, and that she had been very sad to leave the centre," Ms Robinson said.
Parties were encouraged to agree costs between themselves.