There are two artists with this name:

1) Ronny was a french girl, who moved to The UK to become part of the Blitz Kids movement. In the early 80s she worked with artists like Rusty Egan, Midge Ure and Yukihiro Takahashi and released couple of singles. Then she disappeared from the public eye.

2) Wolfgang Roloff alias "Ronny" is a German "Schlager" singer.

1) Ronny used to be a Top French Model. She was brought up in the grim Northern industrial area of France and left home at 14 to go to Paris, there lying about her age and doing terrible jobs. She took dancing classes and jobs, then stopped everything and started to write songs. Club entrepreneur Rusty Egan met Ronny in the Paris club Privelege and co-produced with Midge Ure her best releasel; Vangelis, Georg Kajanus and Peter Godwin also produced for her. Ronny, a masculine name, is the blitz girl who loved to dress up as a man. She also appeared on the Ultravox ‘Station’ record sleeve.
More info:
http://vzone.virgin.net/sam.vox/html/ronny_solo_singles.html
http://www.geocities.com/theblitzkids/ronny.html

2) See Wolfgang Roloff at german wikipedia http://de.wikipedia.org/wiki/Ronny and at his german fansite http://www.ronny-fan-club.de/. Read more on Last.fm. User-contributed text is available under the Creative Commons By-SA License; additional terms may apply.