Under a hundred dollars is where most jewelry gifts should live. It is enough for a real piece in a real metal, and not so much that the gift arrives with an obligation attached.
Spend it on one piece rather than two. One well-made everyday piece will be worn more in a year than a pair of lesser ones combined.
Necklace, earrings, or bracelet at this budget?
A necklace, for one practical reason: it does not need to fit. Bracelets and rings need sizing, and getting it wrong turns a gift into an errand. Earrings are the second choice if you know her ears are pierced and what she usually wears.
Should I spend the whole budget?
Not necessarily. The right piece at seventy dollars is a better gift than the wrong one at ninety-nine. Choose the piece first, then check the price.