maybe we could see a full body pic of her?
That would help us be able to tell better.
From what I can see of the face i'll say this:
LEAVE her mane and tail. Arabs and welsh both have long mane in the show rings, so that's not a big deal.
From what I can tell from her FACE I would say trim the legs.
But I would need to see her body, if her body is more arab-like then I would trim them. If she resembles the welsh more, then I would leave the feathering.
GOOD LUCK! =]
You can tell a gelding, you can ask a mare, but you must discuss it with a stallion.