Hi Andy, if you've seen one on the beach then maybe you could ask the owner if you could have a go if they are reluctant try lending them your board and ask them to compare the two.
The Atom is not agressive at all, very dosile and it is the Atom that is passive planning.
I would say for sure that if she is less than 75Kg then go for the 100.
2011 Neil Pryde Atlas 4.2 & 4.7, 2015 Ryde 7.5 & 6.5, 2014 Severne Overdrives 7.0, 7.8, 8.6 & 9.5
2015 Starboard Kode 86L Freewave, 2013 Fanatic Skate 109L, 2014 Starboard isonic 110, 2014 Starboard AtomIQ 110 & 2014 Starboard Ultrasonic 147