Yes, Radha Devi is considered to be the avatar of Laxmi. Radha is also known as Mool Prakriti and the Supreme Goddess. Radha is the female counterpart and inner power (Hladini Shakti) of Krishna. Radha accompanies Krishna in all his incarnations.
Some more things about Radha and Laxmi:
- Radha is considered to be the goddess of love, tenderness, compassion and devotion.
- Radha resides in Golok.
- Radha Rani is the cause of the origin of Maa Laxmi but is not her incarnation.
- Maa Laxmi was incarnated from the little finger of Radha Rani.
- The incarnation of Maa Laxmi can be said to be Rukmini Devi in Dwapara Yuga and Sita Mata in Treta Yuga.
- Rukmini is also considered to be the incarnation of Laxmi, the goddess of fortune.
- Both Radha and Rukmani are parts of Maa Laxmi.