No. Agnetha Fältskogdidn't do nude photo's. However, there is one picture that was taken at the Unicef gala in 1979 where ABBA were in attendance. A photo of Agnetha arriving at the gala wearing a black see through dress. Her left nipple is clearly visible as she's not wearing a bra. This photo has been edited (made darker) with Photoshop. However, it can be re-brightened to show all the detail. ;O)
