I wasn’t questioning that she was right abut the apostrophe. I was just taught to write out dates in a letter.
Oh, sorry! I was taught that also, but in today’s world, I”m learning to dumb down my writing. No more writing out numbers one through ten, now it’s all just 1-10. I still don’t automatically find the numbers on my keyboard.
There is a tie when numbers look fine in a statement, other times it looks much better as spelled out words and you can definitely tell when one is preferable to the other. If it looks stupid, don't do it.