I had a grade 4 placenta praevia with my second son and would agree with kimberleyj in that you you do think very long and hard when you're at very real risk of losing your baby (and your own life) so please don't think your sister's making a bigger deal of it than it should be. I was terrified.
That said, I'm a nurse too and worked until I was 33 weeks, I was told that although bedrest was what they used to recommend it wasn't the case now and that it really didn't make any difference in the long run. Everyone's case is different though and I didn't have any contractions or cramping at any stage and didn't have a bleed until I was 35 weeks (and what a bleed, if I wasn't terrified before I was after that).
I don't really have any advice, just a pov from someone who's been there.
3b in South Australia.