V4 will work any version of Poser you're likely to have. She'll work fine in Poser 5.

If you're really, really patient, DAZ puts her on sale for free from time to time. If you want her now, they're having a pretty good sale this weekend. Discounts on a lot of DAZ originals, and an additional 30% off applied after you put the item in the cart. Check out the various Victoria 4 bundles if you're interested. It's often cheaper that way, and you'll want her morphs and a texture or two.

V4 comes with a V4 to V3 figure (like V3 had a V3 to V2 figure). It's basically V4's head on V3's body, so you can use V3's clothing on it.