Dear [Relative's Name],
Thank you so much for the lovely gift you sent me for my birthday. I really loved it, and it means a lot to me. Also, thank you for coming to my birthday party. It was such a pleasure to have you there, and I enjoyed our time together. Your presence made the celebration even more special. I hope you had a great time as well. I look forward to seeing you again soon.
Best wishes,
[Your Name]