Isn't Katherine supposed to be in love with Stefan because Quetsiya said she saw the two of them over and over again they always end up together. Since Katherine never ended up being with Stefan isn't she the one who suppose to be with him and that means that another dobblegangger of stefan would be created to fall in love with Elena.????
Actually I believe that Katherine and Stefan are suppose to be together.
Stefan's personality is not simular to Silas and Amara from inference from Silas and Tessa is more like Elena than Katherine. So Stefan doppelganger should be a shadowself Amara. Elena is a doppelganger of Amara but she is not a shadowself of Amara. Katherine is a shadowself of Amara,
Shadowselves personalities are more different than the previous selves. i.e. Amara=good, unknown doppelganger=bad, Tatia=good, Katherine=bad, Elena=good.
A good doppelganger (Stefan) connects with a bad doppelganger (Katherine).