I think it is rather simplistic to label anything negative a new mother does as "not being able to handle the pressure" given the HUGE amount of hormonal and brain chemical changes a new mother undergoes shortly after birth. This is a VERY REAL change and, if the mother doesn't get professional help, it could end up permanently changing her personality and behavior. So, no, to say she just couldn't hack it is a case of either lack of experience with new moms on your part or lack of empathy. I was fortunate to have foreknowledge of this when my wife gave birth and knew what to look for; we didn't have anything beyond a very mild case of it. Having said that, there could be other circumstances involved here, but the story would seem to indicate PPD as a contributing factor. Here is an article on Postpartum Depression.