Use the V3-to-V2 character included with your purchase of V3. She's designed to have the same body shape and joint parameters as Victoria 2, and can wear the older clothing.

V3 body morphs won't work with the V3-to-V2 character, but head morphs will.

If you also have a copy of Victoria 1 or 2, download the V3 hybrid figure from Netherworks Studios. It combines the older body with the new head, and can use V1 and V2 body morphs.