story identification - Trying to remember a fantasy novel with a fighter/thief female couple and an "X and Y" title

I was answering a question on TVTropes and I was trying to remember a fantasy novel I read in high school (1990s). The main protagonists were a thief with metal nails (she got them via some sort of magic. The metal in them was drawn from her body, so she had to regularly take doses of fish oil to prevent anemia) and a warrior, both females. I remember a scene where they compare knives and trade, referencing the superstition that a gift of a knife is bad luck. During the same scene, I also remember the warrior admiring a composite bow. There's a later scene where they barely manage to escape some sort of candy factory, resulting in a fairly tame romance scene where they remove the hardened candy (caramel?) from each others' bodies. I remember that mention was made of how the skin was burned, but not too badly, under the candy shell.

The title was one of those "X and Y" deals, something like "Lace and Steel" (and yes, I checked for that title) and it had the two women on the cover, looking off to the side on a street corner, the thief crouched and the warrior standing.

Answer

Saber and Shadow by S M Stirling and Shirley Meier.

This is the second book in the Fifth Millenium series. The reference to fish oil is right at the start when Megan Whitlock is enslaved in a galley:

Then, she'd been able to feed herself things like fish oil so that the growth of her claws wouldn't leech her blood of iron. The witch/healer who had given them to her had explained that it would strain her body just to have steel claws, that she would have to guard against blood-weakness by eating liver and fish oil.

I skimmed the first book, Shadow's Daughter by Shirley Meier, but I couldn't find any mention of how Megan got the claws.