The lighting is likely not too high. Flow could be a reason, but:
Some times one of the heads die off from damage of taking it home or while on transit to the store. Or it coulc have just been mishandled at the store or set too closely to another coral and recieved a nice protozoan infection from being stung and wounded.
Yes too much flow could have killed it, but that usually looks more traumatic with flesh ripping or it will shrink up and try to protect itself.
Either way as long as the stalk dies off completely and does not leave behind any "brown jelly" the rest will be fine. I would not cut the dead piece off because I would say close to 80% of the time you will get new buds or even the same head to grow back with in 2 months, IF you do not move it. Normally when you see a Euphyllia (Hammer, Anchor, Torch, Frogspawn, ect) that has a lot of heads and has babies growing from it, it is because it hasn't been moved alot. Once these corals feel like they are in a safe spot and remain undisturbed they will be very prolific, but it takes a few months.
As the the gender confusion of the coral: buy it a couple drinks and when it's not looking take a peek under it's skirt.