In laws...

So today my kids biological mother showed up for a visit after almost zero contact for 5 years. Well while she has been here my kids ( I have been their mom for two years) started calling me ms."my first name" ...they havent called me that since my husband and I got together.. when my husband asked our daughter why she called me that she said that my mother in law told her that when she talks to her "real mom" that she isn't allowed to call me mommy anymore. I'm hurt and I'm angry and I cant believe that my child is being told not to call me mommy just because they dont want to hurt the other womans feelings..this is her first visit in 5 years and she only calls once every couple months sometimes once a month. Am I wrong to be angry at my in law?