If it's only a leave then she will not be harmed and as she is still in veg she will push some new ones so no need to worry
Since you have no light related issues and because it is an auto you can continue with the 20/4 light schedule , generally it can create some cal mag issue but your nutrients line have enough inside
You're alright! Internet wisdom says to not or minimally defoliate autos, but a broken fan leaf is just going to happen occasionally.
I'm actually a week behind you with a RQS Northern Lights auto, looking forward to watching your success!