You need to do two things, Leigh. One, find the right boot. Two, stabilize that bad ankle past what a bootany bootcan do.
As for the boot, youre looking for a light hiker that offers reasonable support and good traction. Lots of choices there. Asolos Echo boots ($100; www.asolo.com) are just the ticket: light, reasonably breathable, with good traction. An over-the-ankle design also offers more support than low-cut hikers. For a little beefier boot thats still very comfortable for day-hiking, try on the Montrail Solitude II ($140; www.montrail.com). These have the advantage of one-piece leather uppers, a more durable, more weather-resistant design than boots that are pieced together from several bits of material. And, the Solitudes are fitted on a womens last, meaning theyll fit better than some boots that are sized for women but not really designed for women.
I really dont think you need waterproof boots (the Solitudes already are very water-resistant), but if that seems appealing to you, Zamberlans Micron GT Hiking Boots ($150.00; www.zamberlan.com) have a Gore-Tex liner to keep just about any water outunless you step in over the boot tops!
None of these boots, however, will hold your ankle in place if you really start to roll over on it. So buy a good-quality brace, such as the Swede-O Inner Lok 8 ($45; www.swedeo.com). Its a lace-up brace made of non-stretching material, so once its on and secure, its almost impossible for the ankle to rotate sideways. And it will fit under most footwear (not allbuy a brace, then shop for boots). Several models resemble this one, so dont hesitate to try a different brand. But it must be a lace-up brace made from Cordura or similar tough material; a stretchy, elastic brace wont cut it.