I've learned a bit about NJ practice but I was told NY is pretty similar.
You might have a tough time claiming adultry after a seperation, unless you had reason to suspect it was going on prior to the seperation and was just now brought into the open.
You would probably be better off claiming extreme mental cruelty and using the suspected adultry to support that (then you don't have to prove it, just give a legit reason why you suspected it, that's how it works in NJ).
It might also make a difference where the relationship is taking place, did the other party bring their new partner into the martial home?
EDIT The new info makes a world of difference, you're friend should be okay. But why is she waiting for the full year seperation, that'll be more of a hassel down the road (especially when sperating their assets). She should file a complaint on extreme mental cruety gorunds and get it over with in 3 months or so.