The objection to the word is not linguistic. It's just a strange word to use about your daughter. Firstly, it's very biological and cold. Secondly, it is a description of what the male (the boyfriend) did, not the female (the daughter). It means to MAKE pregnant, not to BECOME pregnant. This could be viewed as objectifying the girl. It makes her less important when she is actually the most important. It is also true that the correct form would be 'impregnation' but that is not why the word is considered "off".

In that sentence, it should say “an accidental impregnation”