Should I write a letter to Walmart's corporate office?

You see my mom went on the 10 items or less line even though she had 28 items. She did this because the light wasnt on and because the lady in front of her had over 20 items therefore she figured the rules didnt apply. Also that was the only lane open besides 25 items or less she would have gone in that one but the line was to long! It seems ridiculous to me that that they only had to lanes open! Anyways from what i hear the cashier wouldnt let her buy those items there because they were to many but she had no problem assisting the other lady in front of her with a smile!? My mom is a really nice person and an excellent customer she bought like 70 bucks worth of things all she wants is to be treated fairly is that so much to ask? And more registers should be open. So should I write a letter to corporate stating my problem? Any ideas you can give me to write a good letter to corporate? thanx again! :)