The heavy deluxe items are larger in ever respect; they have a wider strap, which makes them look chunkier (you can see this in the product photos where the cuffs are on a model), and they have a larger sizing, e.g. the heavy deluxe wristcuffs have an internal size of 6 - 9.5 inches whereas the deluxe cuffs have an internal size of 4-8.25 inches.
I own the full cuff and collar set of the regular Deluxe and personally, I'd say go for that if you are planning to use it on a female partner as to me the heavy deluxe items would look too big/chunky on a female frame (the regular deluxe already look chunky) and would possibly be too big to fit securely on her. It's a great set, it fits both me (a female with slim wrists and ankles) and my partner (a male with much chunkier wrists and ankles) so if you ever want to switch positions it should fit you fine too.
The regular Deluxe items have a padded, chunky look and heavy but comfortable feel to them, if this is her first time using cuffs she may be overwhelmed already by the thickness of the deluxe and the stiff new leather so the heavy ones could be a little bit too much and put her off them.
If she has a particularly slim or short neck or hasn't worn a collar before I'd reccomend going for a slimmer collar than the Dominix Deluxe one, though. I find it a little too chunky to be comfortable, it restricts my head movement and can make me feel too restrained and panicky. This one is on sale atm and would match the Dominix cuffs: