What gift a friend's girlfriend gives for her birthday can be decided according to her interests and preferences.

If she likes jewelry, consider giving her a beautiful necklace or earrings, or a high-grade bracelet, ring, etc.

If she likes traveling, she can consider booking a trip or staying in a high-end hotel, or taking her where she wants to go.

If she likes reading, consider giving her a book she likes or a book she wants to read.

If she likes delicious food, consider sending her her favorite food or dinner in a fancy restaurant.