I highly recommend Aquamedica! It's located at Pier Village in Long Branch. It's right on the beach.... and there's restaurants and shops. She can make a day of it.
Their website is
www.aquamedicaspa.com (http://www.aquamedicaspa.com - broken link) and you can get gift cards online (and I think you can even print them out if you prefer that over getting it mailed).
Check out
www.spafinder.com for reviews on spas in the area. I think
www.spawish.com is another resource.