I'm surprised no one has discussed the possibility of suffocation, this is how babies have died in the past in the US. I will concur that your concern should not be that the snake would eat the baby (although it is certainly not 100% impossible, humans are mammals and are potentially food - especially little humans). However, I recall reading in one of my reptile books about a baby that suffocated as a result of a large constrictor getting loose and crawling in the crib with the child. Of course, the snake sees the child as a heat source and the baby dies as a result of suffocation. And of course, there are lots of posts on this forum on how to find snakes that have escaped so no one here can contest that snakes escape despite our best efforts.
So, I am not going to tell you not to worry about it; it's unlikely but not impossible that the child's safety is at risk. Therein lies the fear and your girlfriend is justified.
You can take all the precautions you desire but accidents happen.
Just being a realist....