Not familiar with IT, but if I had to a team to work on/

with an extremely demanding job/boss/client and an imminent deadline, I'd push my team hard and let them share my burden and stress. Unless you know your team-member really well (which I don't think you do, as the girl is new), I think you have to keep a close eye on them under such circumstances, because the tolerance for error or slack is slim or null. Don't feel bad about it, just let your subordinates know that, if one thing screws up, the whole team will lose, you are all in the same boat.