everytime my mom gives me a motherly reminder, I stop what I am doing, look directly at her, and say "Thank you for that reminder.", totally deadpan. Then I continue what I am doing.
IMO, if you chastise her in front of others, it will only serve to reinforce her childish perspective of you. And if you pester her to stop in private, it will only serve to reinforce her childish perspective of you. (see a pattern?)
Tell her once to stop (ok, a few times if necesary), then realize that she can choose to respect your wishes or not, and you can choose your reaction to her every time she says something (ie you dont have to get aggravated, you can just let it roll off your back).