This is easy to handle. Let's have a romantic party. At her birthday party, he will make some preparations first, of course, cakes. Then, he will fill the room with balloons (filled with hydrogen, otherwise it will not float), hang a sweet card written in advance on the rope tied to the balloon, and hang the ring on one of the balloons. On his birthday, he promised to surprise him, take her to the door of the room and kiss her. Bring a big bouquet of roses!
You don't have to show it to her, but keep it well and don't throw it away.