haha that was me. i doubted i had sleep apnea, but when they came in and talked to me I averaged 66 times an hour and as many as 87. i couldn't believe it. I knew mine would be a 2 night stay if i had apnea, just because it is easier on them that way. If you don't fall into a deep enough sleep fast enough the first night then they can't put the machine on you. Your next study they will start you on the machine from the moment you get into bed.
As for your sister. anything averaging under 5 events an hour is considered normal. Most doctors don't treat it if it is under 12 events an hour unless they have severe apnea while in REM sleep. Which REM is typically where people will have the most events because the throat is the most relaxed and is most likely to "collapse", since it is the deepest sleep. She will have to wait to hear the results from her doctor, most sleep techs know what is significant enough to put one on the CPAP, but insurance can be different about what they will insure. My plan pretty much just says "if the doctor thinks it should be treated, then we will pay for it" about sleep apnea.
anyway.. lol now that i have written you an essay i guess I should quit, but good luck with your CPAP Tritation!