Though we get less info from scriptures about Radha, here is an interesting story.
Brahmanda Purana
This Purana talks of Parashurama doing tapas for the grace of Krishna and Shankara (along with their wives!). So the four deities - Krishna, Radha, Shankara, and Parvati appear in front of Parashurama. What does Parashurama seek from Radha and Parvati: In whatever thousand births I take, please ensure that I become the devotee of you four - Krishna, Radha, Shankara, and Parvati. He also admits to seeing non-difference between all four!
Brahmavaivarta Puran:
The Radhikopakhyana occurs in the 48th chapter, where Narayana tells the kathaa. He narrates the discussion that Shiva has with Parvati. When Parvati asks him about Radha and her origin, though the story is extremely secret and not so easily found in Puranas, Rudra meditates on Krishna and tells Parvati that Krishna had asked him not to tell the story to anybody, but since Parvati is arthangaswarupini he will tell the story since Krishna has given the permission. Rudra also says - This secret story that I know, is not known by Brahma or Shesha!
Shiva also proceeds to caution us - Doubtless, one must take Radha's name before Krishna's name! otherwise, they will obtain brahmahatyaa dosha.
There was another story in South India which gains prominence after Jayadeva's Ashtapadis is --
Nila Devi was Radha's elder sister, who was married and staying in Mathura. Once she came to Brindavan to visit her parents. She saw the prominence of Krishna and heard many of his leelas from her sister Radha and from other Gopikas. She argued with Radha and tried to infuse some logic into her mind by questioning every divine deed of Krishna--- Why you are all adoring a butter and milk thief so much? Thieves are punishable in my Madhura, here it seems you are all praying for the attention of a sinner?!!
Grabbing young girls' clothes from bathing Ghat and watching the young girls in their nude form, and teasing them, is it divine Leela to all of you? If such a thing happens in our Madhura, our king will punish such an offender by plucking his eyes!
Why are you praising a dancing and singing kid as a Divine Avtaar? Are you mad Radha?
Then Radha pleaded Neela to meet once her Krishna, reluctantly she agreed!
When the first time she saw Madhav, she lost the presence of all her senses, eager to run towards him, to hug, to kiss, to be with Him for a while. From a distance, Radha was watching her with an inquisitive smile, later she asked her sister, why she was stood before him like a mute doll?
For that, with a distressed voice, Neela asked her --- will your Krishna like this dark girl Neela as he likes you? Ever he loves me as he loves you all? I don't want to go back to Mathura, I want to be with him, I can't leave him, such a mesmerizing youth he is, no, he is not a kid, he is my beloved now, Radha, now I admit that he is God, please arrange another meeting with him tonight!! she pleaded.
There is no authenticity in this story, but I like this story, so I've shared it with you all. π