Here's something I've never seen before - a nail ring. Get one, get a few. Looks like they come in four designs. Probably should order quickly to get in time. Sizes look adjustable.
Order through EverMarker.com and get 20% off as of the time of publication. $15.95 each instead of $20. Really unique without breaking the bank. Notice some are more square at the tip, some more pointy - may not matter but take that into consideration as you look at what she does with her own nails to get a clue what she might like.