If you want to invest in one that will last and is super quiet,
Super Silent Air 20A
its the one i been using for years. Its a work horse and quiet to this day with no issues. Has the moisture trap and is a oil compressor which is not a big deal and doesn't smell. She will be able to airbrush at night without waking anyone up and doesn't vibrate.
I did some videos on it.
http://www.youtube.com/watch?v=JVt6UGaAsok
http://www.youtube.com/watch?v=DTO0_IZw0OQ
now its not cheap tho, if your lucky can find it under 400.
Now there is some others out there smaller and cheaper, but after all my research and actually getting to test a silent air back in the day i went with the 20A.
Stay away from the $100 or under ones that are auto shut on and off, they are loud as hell, vibrate and won't get you a steady stream of air. You need to get something with a tank and that will last.
With compressors you get what you pay for