It would only be idolatry if you believed Mary’s spirit actually inhabited the ceramic statue, or some such nonsense.
Assuming you don’t believe that, then I would see a bow as simply a gesture of respect. I personally do not bow to statues of Mary because in my culture, a bow is reserved for Jesus the King, especially if one is female. A man might bow to a lady in the old timey etiquette of 100+ years ago; a lady didn’t bow to people, she would curtsy or perhaps nod. I would certainly kneel before a statue of Mary, with the understanding that I am kneeling in reverence to Mary herself and not to the statue and that I don’t believe Mary is inhabiting the statue itself.
There are other cultures where people of both genders bow as a greeting, just as a sign of good manners and respect. I have been in a whole church full of people who expressed the sign of peace by all bowing to each other. I would imagine they bow before the statue of Mary as well as a way of showing respect to Mary, again not because they think her spirit is in the statue.