Verified answer

Yes I am. But why are you asking in the classical music section? ABBA is pop music and Agnetha is a pop singer. I'm answering this because I also answer questions in the "singing section".

It would be hard to determine her true vocal range based on ABBA songs which simply don't require a whole lot of range in any of the parts even if the group is known for their rich harmonies. There are a lot of really wild claims (as usual) on Youtube about her vocal range which literally included words actually spoken (but not sung) and a couple she screamed or shrieked so horribly she sounded like someone stuck her with a sharp pin (they sounded better in the studio where it could be electronically edited).

https://www.youtube.com/watch?v=N4lNdora_PU

Most of her actually singing seemed to lie within the range of a typical contralto, but she also tended to sing mostly in her chest voice and usually kept her highest "belt" notes between Bb4 to C#5 (and occasional D5). She occasionally sang as high as an E5 before the notes started to sound a bit "iffy". There are some F5 that really don't sound that stable (probably because she is used more to belting than using a head or mixed voice properly).

She also sang Mary Magdalene in "Jesus Christ Superstar" in Sweden, which is basically an alto/mezzo-soprano role (lies lower than higher really).

Because her voice does have a brightness to it, I'll go ahead and call her a mezzo-soprano. She does do the higher female vocals in the group.

Even if she was a true soprano (which I doubt because the higher she goes, the worse she sounds), pop singers tend to stay much lower in their overall vocal ranges because of the style of the music.