Don't panic too much Plums, I wouldn't recommend keeping horned and non horned together especially, but I know people who do and they don't have huge difficultly. I wouldn't try and take her horns off now, although I believe there are some chemical ways of removing horns but I don't know how good they are. If they get on well enough then they should be ok.
I particularly don't approve of horned pygmies being kept with adult large sized goats. That makes them just the right height to catch a big goat's udder, belly, or other delicate areas!
Beth