Are you sure she was eligible to file I-485 at the time she filed? Whether her I-130 was approved or not is not relevant. What determines whether she can file I-485 is what her priority date was (i.e. when the I-130 was filed) and whether the USCIS visa bulletin chart for the month she filed showed that her category and priority date can file AOS. What was her priority date (the date her I-130 was filed)? When did she file I-485?
How long I-485 takes depends on many factors. For one, the I-485 cannot be approved until a visa number is available for her priority date according to the Final Action Date chart in the Department of State's visa bulletin. (In some months, USCIS uses the Date for Filing chart for AOS filing, and in other months, USCIS uses the Final Action Date chart for AOS filing. If she filed in a month where she was able to file because they used the Date for Filing chart, it could be a long time before the Final Action Date chart reaches her date.)
