But it found that the nursery, which follows Lubavitch teachings, had not shown there was any occupational requirement for teachers to abide by its religioius standards.
Ms de Groen married her boyfriend last year.
Her case is being supported by the Equality and Human Rights Commission.
“No one should be discriminated against by their employer because they do not share particular religious beliefs,” an EHRC spokemsan said.
"We are funding this case as we believe that the nursery could not justify the idea that the employee’s living arrangements had any impact on her ability to carry out her role as a teacher."
Gan Menachem was represented at the appeal by John Bowers QC and Ashley Serr.
The appeal tribunal’s decision is expected to be delivered in a few weeks.