You would think that a hijabi can't wear a mini skirt...and you'd be 100% correct if you were reffering to the normal way it is worn around the world. But there is a new mini skirt out there that is, in my opinion, the best way to make your outfits longer :)
They have an elastic band around the top so you can easily slide it on, and keep it on, but they flare on the lower half so it isn't tight. You would wear a top under, the mini skirt on top (a little below your chest and little above your hips), and skinny jeans/pants under. This creates an illusion that the skirt and top actually is a long one peice top.
You can get them in any girl stores in America and Canada as far as I know. They are super handy, I myself have about 4 pairs. You can get them in any color, pattern and design (flare fit, straight fit, tight fit..we don't really recommend the tight fitted ones).
You can wear a long sleeve T under or a tanktop or t-shirt then a cardigan on top. You can wear skinny jeans or straight legs under because the skirt usually comes up to a little above your knees. Its fashionable and modest. You should wear a pashmina type scarf or a wrap around on top to cover your chest area if the top under your skirt is tight fitting. Dont forget to accessorize!
Below are some pics to show you what I'm talking about: