You really should try to get the ambient temps up ASAP. With the temp going as low as 73, it can cause an RI if it has not already. Also higher humidity (more like 50-60%) would be better. If you can't get the humidity up, a humid hide is an acceptable alternative, but there really isn't any acceptable alternative on the temps.

Some times BPs will have a whistling sound when they breathe for reasons other than an RI. If she is either about to shed, or has just shed, it might be a bit of shed in her nostrils.

If it were my snake, I would bump the temps up to about 85 cool side/95 warm side, and watch her very closely for a few days. At the first sign that the RI might be getting worse, or if it does not clear up right away, I would take her to the vet.