How can i fix or ease this family situation?

i live w/ my son, his wife and their 2 yr. old. I have no option of any other place to be, and i am blessed and thankful to be here everyday w/ my granddaughter, especially, and my son/wife. My daughter-in-law is an exceptional mother at 20 yrs old, and i tell her all the time. but it seems anything and everything i say about or to the baby is wrong, and i do get told about it. so i really have tried to change my personality (i guess is the word) or habits to make her happy. i also babysit the baby most every day whlie they work, which i love. one example is last night mom was changing baby on the couch, and baby had her toothbrush and was attempting to brush her teeth. I came into the room and the baby got very excited and starting bouncing on the couch with the toothbrush in her mouth. all i said was " you know "punkin", if you keep that up it might choke you". mom took offense saying that she was right there and could handle it, and i have to let her raise her child and that comment made her feel like a bad mom. to make a long story a little shorter, i reminded mom she was exceptional mother, and told her that my comment wasn't meant to reflect on her, that i was "talking" to the baby, it was just a comment. she said that my comment was unacceptable, and i better think things through before saying them. i've worked customer service all my life, and i've seen hundreds of mothers and babies. i have made plenty of comments like "you have a little red nose, it must be cold", the mothers never flipped out on me ever. i've never had to walk on eggshells and worry about what i say will start an uproar. I was brought up with manners and think i know what is appropriate and what is not. any suggestions on how to keep things happy? was i wrong in this case? It has been an ongoing problem, and i do love the mother, as i would a daughter. HELP!