One of the texts that mentions Maa radha is Garga Samhita ( A treatise written on Lord Krishna’s life by sage Garg). In this maa radha says that her darshan is rare.
Garg Samhita Further mentions Rādhā-Krishna Vivah
Narada pancharatra Says Maa Rādhā is the Goddess Maha Laxmi and Maa Saraswati.
Lord Krishna is referred as father of universe while Maa Rādhā is referred as Mother of Universe.
There’s a Rādhā Sahasranama stotra in Narada pancharatra as well.
Narada pancharatra also has Rādhā Kavach and her mantra
As per Brahma vaivart purana Maa Radharani is one of the 5 Goddess of Prakriti.
Brahma vaivart Purāṇa Says Lord Krishna is Maa Rādhā’s everything.
Maa Rādhā doesn’t want to be separated from Lord Krishna for even a single moment.
Lord Krishna says that He is nothing without Maa Rādhā and She is dearest to him.
While Padma Purana mentions Radha Ashtami another text called Skanda purana mentions Radha maa properly.
Both Nimbarka sect and Gaudiya Sect Worships Rādhā-Krishna as well.
Conclusions :
1 Maa Rādhā exists and can’t be separated from Lord Krishna.
2.Her appearance is referred as Lotus like
At the end i will just say:
Mithe Ras Se Bharyo Re,
Radha Rani Lage,
Radha Rani Lage.
Mane Kaaro Kaaro,
Yamunaji-ro Paani Laage.