Heat stress or Root rot ??

That looks like a mutation to me meaning a bad seed in my experience yeah your right with the light and heat stress that is causing some of the damage but I would assume this is just a bad seed by the plant structure anyway. lift the light higher try keep temps down. maybe try and flush her out but not much you can do really the lighter leaves at the bottom is showing slight N defienancy other than that she is healthy enough but i bet she is also going slow aswell ? if so then yeah its just a bad seed she will finish and give you some kind of product but will it look pretty probably not lol. best of luck my friend your plant your choice shame to loose the wasted time though. keep up the great work bro we all have these problems now and again thats why most growers always pop more seeds than needed :)