I think how much is visible during breastfeeding can depend on one's size and shape, and maybe the size/position of the baby. I usually found that I didn't need a cover to avoid showing anything dicey while nursing. I did, however, use a cover at places like church or when men were around, so it didn't make them uncomfortable worrying that they'd see something they shouldn't. However, the phrasing "whipped it out" implies to me that she didn't keep things hidden by her shirt above, but instead exposed her entire breast in doing so.
Putting the baby on the table is disturbing. I'm not clear if Marina was holding the baby or just sat the baby on the table and hoped she wouldn't fall off. But it's weird. I sometimes don't bring a seat or anything for a baby, but then I'd hold the baby in my lap.
Chewing on a religious artifact? Was this yours, or hers? It seems needlessly antagonistic even if it was hers and she brought it, as it might bother others of the same fate. But then, just about everything she did seemed needlessly antagonistic.
Everybody has already said my thoughts about the conversation monopoly. Does she have aspirations to be Lady Catherine de Bourgh?
For changing the diaper on the floor, I can see it possibly being her usual habit. Once you're accustomed to diaper changing, your baby is no longer a newborn (and so blowouts are rarer and peeing/pooping *during* the changing almost never happens), and your baby is still young enough not to fight you too much, it's not really difficult to change a baby without a page, simply by putting the new diaper *under* the old one, so that it sort of acts as a mini-changing pad. Unstick old diaper, open, lift baby up by legs to clean baby, fold up old one, put baby back down on new diaper, stick it shut. Nonetheless, this is not a risk I'd take on anybody's carpet, including my own! I'd aim for a tile floor if there was no other option (there's a changing pad in my diaper bag, though, so it's never been a problem). I'd guess that she was putting the baby's comfort (nice soft carpet instead of cold hard tile) over everybody else's.