The answer to your question is a little complicated, and I'd need more information to do a good job, but in a nutshell that oxygen level is too low. Is she on oxygen with that level? Because that would be worse than if she is just breathing room air and sick with that level.
Usually we like to see a level of 92 percent minimum on room air across the board for a typical person. Why was she taken off lasix? It really is hard to fully answer without more details. If a person is at home with CHF and an oxygen saturation level of 82-87, that person should get medical attention as soon as possible.
We have some information on CHF: https://www.empowher.com/media/audio/audio-dr-bove-congestive-heart-failure-heart-getting-stiffer and the National Institutes of Health has a nice tutorial as well: http://www.nlm.nih.gov/medlineplus/tutorials/congestiveheartfailure/htm/index.htm
I hope this helps.