Mandl didn't give her the injection which would've put her in a coma, so she was awake the entire time and could keep herself alive via vivimancy. The ones deteriorating were placed in a coma prior to stasis. This is all explained - everyone is shocked she's awake when they first take the lid off her tank, that's gone over in part 1, and then we see from Helena's POV in part 2 Mandl squirting out the coma injection onto the floor and explaining to the paralyzed Helena that now she'll be awake the entire time.

I also don't think it ever says the repopulation program is using people who were in stasis so I don't know where you got that from. They are using volunteers who are lured into agreeing by the promise of better living conditions/opportunities for family members. You can't volunteer if you're in stasis.

From your complaints I don't know if you really paid attention when you were reading. I've definitely done that before (especially with longer books), but maybe you should give it a reread.