I'd email the teacher stating that you understand she told your child it was unfair for them to get extra time to complete the test. This impacted your child by _____ (feeling sad about oneself, embarrassed, etc.). Remind the teacher that the IEP states that your child needs extra time due to ____ (disability) as it is an accommodation to help them access their education like their non disabled peers. I'd probably CC the principal and the special education case manager so they're aware and can provide training to the teacher.