Communicate with the 5th grade teacher your thoughts on how she reacted to the issue. Explain that it ought to be a non-issue. Maybe you could ask her if she was truly offended, rather than assuming/jumping to conclusions via your ex-bf. Our flag serves as an important historical landmark for the civil war era and the hate that many people in the south and north held and may still hold to this day. It is a good talking point, NOT something that should shut down conversation, but create discussion. Explain this to her and be willing to talk it out.
Tonight was our last family night, and my students were doing “wax museum” type performances based on their state they have been researching. Under a table I had everything my kids would need - the “push here” button, their state suitcases they made, and their state flag that they would hold up.