Macaydia
I think I am the only one here in support of your daughter. I agree with not having visitors for 12 weeks while the child gets used to life outside the womb and the mother begims the long proceas of healing. Having visitors over would probably cause stress for her when all she needs is rest with her baby. The only interference she needs is when her DH is home. I wish the best for your daughter and her child. First one is always the careful one so just allow her to have self-confidence since becoming a mother is a huge step in one's growth. Give her support - not critisism about how she is supposed to behave. A congratulations card in the mail is not interfering with her wishes and also makes a nice keepsake for the baby.
I'm unable to think of any culture now or in the past where a new mum is left free of visitors for three months.
I think it more usual around the world for aunties, sisters, friends and grannies to be a comfort and support rather than a source of stress.
IMO, it is a terrible pity if an expectant mum is reading things on social media which are encouraging this.
I'm sure I rolled my eyes at the odd 'well meaning' visitor now and then, but 3 months of isolation could be quite damaging to a new mum's well being and mental health.