I had leaking waters with DS; this was in the States, and diagnosed at 29 weeks. I was put on bed-rest in hospital immediately, and checked daily for fluid levels. The baby was monitored twice daily, i/v antibiotics given, steroid injections - really detailed care, and I managed to hang on for 8 weeks with just enough fluids. DS was born OK by c/s.
I am pregnant again now, in the UK - 18 weeks. I have seen a midwife, followed by a consultant (v briefly) precisely once at 13 weeks. She was adamant that they would give no extra care or consideration to me before 25 weeks because there would be no hope for the baby even if it was known that my waters were leaking - nothing they could do. She would not be drawn as to what extra care I could expect after 25 weeks.
How much this is a financial decision I don't know. It has been a very anxious time since I don't know what might be happening inside, and won't have any info until my anomaly scan in a couple of weeks.
So sorry to have only depressing news. I can only suggest lots of bedrest, and we'll all be thinking of your SIL.