What will cover this orange?

Well, for what it's worth, it looks fabulous on you.

I'd say it's too dark for a light ash brown to cover it. But to tone it to the lightest it will go, you can just use blue dye heavily diluted with conditioner. It might appear a little darker, but toning anything darker than a yellow will look darker when it's toned to a neutral. It's the most effective way to keep roughly the same depth of colour while changing the tone.

Though, before going and getting blue dye, use some image software and invert the colours. You might need green or a green blue to tone it effectively to an ash, inverting the colours will give you the opposite colour of the tone you have now which is what you need to tone.

Thank you!

How light does one need to get their hair to achieve something likelse a light brown?