If you start shopping for necklaces gifts for her, the first thing you need to consider is the occasion.
Are you buying a necklace as an anniversary gift? Is it her birthday? Or are you just looking to give her a small gift to show you care?
The occasion of the gift will likely guide how much you plan to spend, and may also guide what type of necklaces you're looking at.
For instance, if you're celebrating a special occasion, then a fancier, more expensive necklace might be a good choice. The necklace will become a lasting memory of the special event.
But if you're simply looking for a gift that says you care, something she can wear every day might be a better choice. Don't underestimate the simple gift though. If you put thought into choosing the right necklaces for her, she'll always remember the moment, no matter how small.