Eleonore was the sister of Stephan von Breuning, and a member of the family in Bonn that did so much to help the young musician.
It is almost certain the young Beethoven fell in love with Eleonore as a teenager in Bonn, and quite likely that he pressed his suit (unsuccessfully).
On leaving Bonn for Vienna in November 1792 she was one of those who signed Beethoven's autograph book, quoting from a poem about friendship.
But they had had a serious quarrel, judging by the letter Beethoven wrote to her from Vienna a year later. "Often in thought I have conversed with you and your dear family, though not with that peace of mind which I could have desired. It was then that the wretched quarrel hovered before me and my conduct presented itself as most despicable, but it was too late; oh what would I not give to obliterate from my life those actions so degrading to myself and so contrary to my character..."
She was clearly not overly offended at what was probably a physical attempt to persuade her of his love for her, since in the same letter he thanks her for the waistcoat she gave him -- though pointing out that since it has gone out of fashion he can only keep it in his wardrobe! -- and in a second letter written six or seven months later he thanks her for the beautiful cravat she has made herself and sent to him.
In return he dedicated to her the Variations for piano and violin on 'Se vuol ballare' from Mozart's The Marriage of Figaro WoO 40, and the Rondo for piano and violin WoO 41. He also dedicated to her the Piano Sonata in C WoO 51.
Eleonore married Franz Wegeler in 1802, and after establishing a family they moved to Koblenz. Eleonore added a postscript to a letter from her husband to Beethoven in 1825, imploring him to return to see the Rhine. But Beethoven never returned.
As far as I can establish, he never saw his childhood sweetheart again after leaving Bonn in November 1792.