What would cause the oil light to come on at idle after being driven for a while

Not yet, she had an oil change last week and they didn't say anything about her bein low on oil when they changed it

check oil level!need to check oil once every week!did THEY put right amount of oil back in it when changed?

Oil level is fine, right at the mark, she says it's been doing it for several months, but I drive the car last night and noticed it,

have oil pressure switch checked,also have the oil pressure tested.When the oil pressure is either high or low it will either turn the oil light "on" in the dash or move the gauge to the extremes Undetected high or low oil pressure can result in internal engine damage and/or gasket leakage

Oil pressure test is that the same as a compression test

no.get a mechanic to check it with a manual oil pressure test gauge.

Alright thank you

your welcome.