I would have gone and met the new teacher. If something is important for your children, you put any of your bad feelings aside. Children always comes first. I understand the reaction from your W because this feels like your new activity is more important than your D's hobby. I understand this if your W was going there alone and asking you to join. Be there for your kids to always rely on. They value your presence more than you know and more now than ever.
In my thirties, BDd 2017, divorced 2 young kids new relationship