Good Luck Buddy.
A lesson (NOT TAUGHT BY YOU) is a good idea. Also - bring the twin tips. Mentally prepare yourself for puttering down greens for the day or at least the part of the day she is in the lesson. DO NOT abandone her. Keep in contact via phone.
Do not buy a $100 lift ticket. Go somewhere for beginners. She will likely be on the same 5 trails all day.
Bring a camera. Take her picture.
Frequent Hot chocolate breaks with foot rubs for sore chilly feet are a good idea.
Don't make her ski two days in a row.
Buy her something.
If she is a never ever and is going skiing, it is becausue she loves you. She could give a CR-P about the skiing. Make sure she has a good time. Ski a little. Then surprise her by arranging a couples massage, some wine, a "nap" and THEN a nice dinner. Trust me on the order.
Don't bungle it.