This is something you need to do to honor your daughter. It is only a short period of time and you can probably build up the scar tissue on your tongue by biting it during this brief encounter with your ex. Your daughter has already been torn up by the divorce. She doesn’t need more drama because you can’t control yourself around your ex. Let your daughter know you will commit to being polite so she doesn’t have to worry about it. She probably is and you letting her know she doesn’t have to worry will relieve a lot of anxiety most likely.