On your girlfriend's birthday, you should spend the whole day with her, take her to places she wants to go, play some games she wants to play, see some scenery she wants to see, in short, satisfy all her wishes on this day, let her have a different birthday, and leave the best memory.
In the evening, prepare a candlelight dinner for your girlfriend, with red wine, birthday cake, and her favorite food. In short, focus on her and make her feel like a princess.
As for her birthday gift, you need to observe carefully to see what she likes or what she needs in life, and then choose a birthday gift she likes or needs based on these. Such a gift is the best gift that reflects your concern for your girlfriend and is also the best gift.
The gift recommended to you is blessing chocolate. Write what you want to say to your girlfriend on it and let the sweet chocolate convey your love for your girlfriend.