I think you need to understand the difference between offering tips and advice and demanding they be accepted and implemented.
As with any new thing we do in life those that have experience offer advice. However these bits of information come from many people (all with good intentions) and it is up to the person doing the learning to decide what is important to them.

Keep up the good work Grandma but let the new parents decide.

Be supportive of mom. She will parent her way to her child. Save advice until either asked or it becomes an endangerment issue.

Honestly unless she is risking the babies life (which she is not) I woudl not say anything as you will cause major problems.

Are you talking about the baby being swaddled?

I don’t think swaddling does any harm. Belly sleep is a risk factor for SIDS but swaddling should be fine.

well it is her baby, let her be the mom. you can offer advice, but dont try to do her job. when i first had my baby every one kept telling me things about when they had kids, and it was all old info that has been changed. i know its a different deal here, but think about if it was you, you wouldnt like someone telling you how to do everything with your baby. i would say skip the lil things and remind her of the big things that could really endanger the child ie sleeping on the belly