White rings on a cherry table?

Does anyone know a remedy for removing white rings from the surface of a cherry table? The rings were caused from placing hot paper plates on a table without a pad on it and moisture seeping through the plates and the table cloth to the surface of the wood. Not my table but it belongs to my sister in law, She tried the mayonnaise application with very little change, and she is looking for another thing to try short of refinishing the table. Any recommendations appreciated.

I've done the iron just hot enough to make steam, lay a wash cloth or thick (maybe doubled) piece of t-shirt over the area, apply iron and keep it moving at all times while in contact. No push-button-blasts-of-steam for this, just slow gentle slightly damp heat. Check frequently or the fix becomes the problem .

http://tipnut.com/diy-how-to-remove-white-heat-stains-on-wood-table/
http://www.howtocleanstuff.net/how-to-remove-white-rings-from-wooden-furniture/

Thanks Glenn I will pass along the information

This is a common problem with shellac finishes. If it is shellac, I have heard folks recommend alcohol, just enough to soften the shellac temporarily (don't flood it to dissolve the shellac), and since alcohol absorbs water, to draw the water out of the finish.

The theory makes sense to me, but I have not had to use the trick, so if someone who has used it can add info, that would be good.

I turned a cherry pedestal table for my wife. It is finished with Deft brushing lacquer. Recently my wife put a vase of flowers on it and the vase leaked water onto it. It developed a white ring but it eventually went away on its own. Good luck!