Forget about volumes or width, a fellow windsurfing friend has the Atom 100 and is 75kg and says it is perfect for him. Unless she is planning on using sails bigger than 7m then the 100 would be my recommendation.
For me at nearly 90kg it feels big when using a sub 7m sail and would be too slappy for someone of your wife's weight in anything but flat conditions. Don't think she will disappointed with the Carve either if she were to go that route.
2011 Neil Pryde Atlas 4.2, Fusion 4.9, 5.5, 6.1, 2015 Ryde 7.5m, 2014 Severne Overdrives 7.0, 7.8, 8.6 & 9.5
2015 Starboard Kode 86L Freewave, 2011 RRD 101 FSW, 2013 Fanatic Skate 109L, 2014 Starboard isonic 110, 2014 Starboard AtomIQ 110 & 2014 Starboard Ultrasonic 147