I doubt that Lena is dead. It is possible for her to complete the ritual in prison though using the prison guards. The other Spinnetod, Charlotte I think, was alive for some time for refusing to commit the ritual needed for their youthful appearance. Sally on the other hand we don't know what her reaction might be. She will have to kill to maintain her youthful appearance however.
It is all just her appearance, Spinnetods won't die of old age, until they become of age.