Wow. Granted I don't know the whole story, but something doesn't seem right there. I would have bet anything that the hosptial would have kept her. The purpose of the amniotic fluid/sac is to protect the baby from infection. Will that "seal" compromised, any sort of bacteria or virus could potentially get to the baby, with dire consequences. The amniotic fluid also provides a cushion for baby against bumps and from putting pressure on various things (mainly the cord - it's lifeline for blood, oxygen and nutrients). For these reasons, this is why they say you have 24 hrs to deliver once your water breaks. I understand you said it was a leak and there is still some fluid left, but what sort of measures are in place to monitor this?!?!? The tear could get bigger, break & leak altogether. I suppose there is the off chance that the tear could repair itself and mom could make new fluid (since it is always replenishing), but it just seems like an ENORMOUS risk to take.
If I were your friend, I would head back to the hospital and find another doctor. At least if she was confined to the hospital she would be under constant watch and they could continue to give her antibiotics to combat any looming infection. While it's not impossible for a baby to survive at 19 weeks, the odds are not good. :( But whats done is done, and at this point every day is miracle and a huge advantage should baby come early.