Did I have the right to stand up to my MIL or not?

My mil is staying with hubby and I for awhile. We have a 6 month old son and she's been a big help and I truly appreciate it. Since my 6 month old son can sit on his own she has been telling me when I can and cannot hold him because she wants him to get used to sitting and start learning how to crawl. I know she's trying to help but after I kept quiet about it I got irritated and stood up to her. I should not be told when I can and cannot hold my child. Like I said I really appreciate her helping me so much but I don't think this is fair. My son sometimes refuses to sit and want to either be held or sit up.