Arthur could not help himself; he was her brother, after all, which meant it was his job to say obnoxious things such as, "I'm sure you could find a job with dresses or hairbrushes or something."
Morgana actually would be good with dresses; she had always had impeccable taste. She was also a good hand with a sword, and if she was so inclined, he would be willing to look into whether they could take her on at the range. But, it was more fun to wait before suggesting that.