I wouldn't barge in assuming that she has post natal depression either. Some women can be in shock for weeks after giving birth (it can be quite taumatic for some, even if its a short labour), some can be all of a tizzy with hormones and general aftermath of a life changing experience, and some can just be overwhelmed by the responsibility and the demanding nature of a young baby.
She will have been up all hours of the night, run ragged during the day, and without much rest to switch off. So whatever time you ring or text, its likely to be a 'bad time'. At least until about 12 weeks.