Although I can see both sides, I personally would feel alittle cross at being 'stood up' like that.
Whilst I completely and absolutely understand how tough it can be to organise a baby, and can sympathise with the frustration at people with no kids- People without kids don't and can't understand what its like and one can't really rely on them to understand why baby crying fits take precedence over a phone call etc. And well- they don't know your routine so they arnt calling intentionally to annoy you.
If I were you I would definatly call her and let her know the situation. Its a communication breakdown and not worth losing a friendship over :)