My bff also has this problem. She is allergic to everything but 18k or better gold - well, almost everything. If you absolutely MUST use metal (like for earwires), you can buy niobium at a pretty reasonable price.
Otherwise, most of her jewelry is made from rubber cording, leather cord, waxed linen or cotton, or ribbon. She prefers chokers over longer style necklaces that can be made without clasps, so I do some simple bead weaving for her using stretchy cord or use velvet ribbon. We have also found that basic clear nail polish or clear acrylic spray on the backs of things like bracelets works well for her.
Hope this helps!