
No susan is still 18. Its a confusing timeline issue. When adel died in past life she was 17 and sujin was 18. After adel died she was reborn and has lived 16? years more in second life and so adel was thinking that 16? years more had also pased in her original world and susan would be 30 something. But instead it seems they both 'left' the original world in the same year but were transported to the new world 15 years or so apart. Or at least this is my understanding

You may be right she may be 31 but pretending to be 18 so she can get married easier. As I was reading the chapter I found the wording to be a bit confusing and got the feeling that maybe the translators had a hard time with getting the best translation or it may be just an editing thing that made the wording a bit confusing for me personaly
I don't believe that "saint" is 18 years old. I thought that she is 30 years old. Σ(  ̄□ ̄||)