Tamanna (تمنا) is an Urdu word. Its Arabic equivalent in meaning is "Raja'a" (رجاء), which was the name of a Sahabiyat. It is therefore preferable to use the name Raja'a. However, if someone wishes to use the name Tamanna on account of its meaning, there is room for that as well.
Allah the Almighty knows best.
Darul Ifta Al-Ikhlas, Karachi.
مسند احمد: (83/5)
عن ابن سیرین عن امرأة یقال لھا رجاء قالت: کنت عند رسول اللّٰہ صلی اللّٰہ علیہ وسلم إذا جاءتہ امرأة بابن لھا فقالت: یا رسول اللّٰہ! أدع لي فیہ بالبرکة....الخ