get some cal mag for her, treat a little every so offten if its soil, but if its coco, wait for a coco grower to answer your questionj.
if you tell us a bit about your grow , you will get a better answer
the newer leaves look ok, so it may be a past problem, keep an eye on her.
has this just started happening?
no, thats not from water splash.
has it just started, or was it as the leaf grew it showed up?
its allways best to use cal mag on your plants, they controle the growth
personaly, i would get some cal mag anyway. i personaly wouldent worry about the brown bits, unless it starts to get worse. leaves do all sorts of stuff