Stuck with S+ Frieren?

I pulled Frieren but quit the game when the banner started and could only get her S+.
It seems that I am stuck with her at S+ forever as opposed to someone who never pulled her who could hire her, make her permanent and keep upgrading her hsing those soulstones correct?

Could you confirm if I can upgrade her to paragon ? I think it would he oretty lame to give advantages to those who did not pull her at all in her banner.
Ty