dealing with big mouth

How do you deal with people with big mouth giving suggestions like free candy about ur baby ? I am 33 and it's my first baby. All my friends have babies and I do know what they do . I am not an expert but at this age I did some homework and know some stuff . My mil left her sons with thier father when they were young and went to other country, they only reunited when her sons were 20-21 years. (Her one idiot son is my husband ) I don't care about it but I have to bring it up coz she suggests me like she's a devoted mother and I am idiot . My baby has long hair and it was falling on his eyes , I trimmed it. She's like said it million time how did I cut his hair , I should not cut it for 3 years 😳. She looked so angry , I mean excuse me , is this not my son and I have to take ur permission . Now she wants my son to go swimming at 2