Here are some warm birthday wishes you can use for your daughter's friend:
Casual & Sweet
"Happy Birthday! Hope your day is as amazing as you are. Wishing you all the fun, cake, and good times you deserve!"
Warm & Friendly
"Happy Birthday to such a wonderful friend! You bring so much joy to everyone around you. Have a fantastic day filled with love and laughter!"
Fun & Upbeat
"It's your birthday - time to celebrate YOU! Hope this year brings you everything you've been wishing for. Have the best day ever!"
From the Parent
"Happy Birthday! We're so glad you're in our daughter's life. You're a truly special person and we hope your day is nothing short of wonderful!"
Short & Sweet (for a card)
"Wishing you the happiest of birthdays - hope it's a day full of smiles, surprises, and great memories!"
Pick whichever fits the vibe, or mix and match lines. If you let me know her age or personality, I can tailor something more specific!