Lynch grew up in the UK, where she trained classically at the Sylvia Young Theatre School. Her earliest roles include stage credits that stretched expectations: notably, she played Tybalt in Romeo and Juliet (usually a male role) and Rita in Educating Rita (historically a white role).
Her stage career was met with praise and even a prestigious scholarship. During her time in drama school, she was awarded the Laurence Olivier bursary, a highly competitive scholarship from the London Society of Theatre that recognises especially gifted drama students.