This MiL has intruded on an extremely private situation, a scenario in which the OP, not her DH, was at her most vulnerable, in pain, and understandably didn't want people seeing her in that state. The OP's right to privacy, dignity and her own views in relation to her treatment are enshrined in the NHS's own code of practice. On this occasion this was not upheld.
Granted, these are the DH's children as well, but she was the one giving birth to them. Childbirth is a messy, painful experience and a major medical procedure in the best of scenarios; it's not a spectator sport and the mother is not a spectacle. She was the patient, not her DH, therefore yes, her wishes completely trump his on this occasion. It's outrageous that neither the DH nor the hospital staff have respected her privacy and dignity: the hospital on ethical grounds, the DH on the grounds of common respect and decency. She stated her wishes and they were ignored.
The way in which this OP is being attacked, and especially called names, is way out of line. She had a right to assert her wishes, and she also has the right to be pissed off that they were trampled all over when she was at her most vulnerable.
OP, I hope you're able to move on from this in the way that best suits you. If that means staying away from MiL until your feelings have cooled, so be it. It's important also that you and DH are on the same page when it comes to setting boundaries in the future. Counselling can be a huge help with this, if you're willing to consider it.
Congratulations on your new family.