Work on reading comprehension. Start by re-reading the sentence which mentions only one country (Ethiopia) and gives the rate THERE as 90%. I chose Ethiopia as an example of the lack of correlation between religious affiliation and female genital mutilation, since I was responding to your question: "Do Christians mutilate women?".
Malawi seems to have a lower rate than many countries in that part of the world, but in a country where the practice isn't so widespread as to be the "norm", it's likely to be the poorest, least educated people who are practicing it, so there's more than 18% chance that this baby's mother had undergone it (at least if the father's claim to be unable to afford to feed the child is true).
Raised Christian makes it unlikey that FGM was performed on her. I know, you won't like that answer, but, tough. The facts speak for themselves.