Pre -eclampsia has a few symptoms other then swelling and high BP and can be dangerous as it leads to eclampsia here is a link to the BB artilce

I had a very rapid onset within a few days my BP went through the roof - although the swelling started about a week earlier. they did some emergency blood tests at my antenatal at 36wks and I was induced immediately. I'm not sure what they were looking for - something to do with protein I believe???

I can understand what your sister is feeling. I went to my dr on the friday who was concerned about the Bp and swelling told me to come back on Monday for monitoring - did the baby stress test and BP/blood test etc. That weekend I never told anyone about the concerns. My feet blew up like balloons and I had constant headaches and I looked like CRAP! My face was all bloated and drawn - yuck! But I was having enough of a problem with their being a problem without everyone else stressing about it too.

Maybe try talking to your sister calmly about why she doesn't hink it's a problem??? How far along is she?