Only Electrolysis is permanent, but you must find a well qualified practitioner to do this work.
Of course, since you failed to enter your location information in your profile, we are unable to direct you on who might be good in your area.
I would also look into anything that might be making her grow excess and/or dark hairs, so that if there is a way to stop something in its tracks, you could do that before any real trouble came up.
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Setting a goal is not the main thing. It is deciding how you will go about achieving it and staying with that plan. --- Tom Landry