Is it permissible to breastfeed a girl who is a year and a half old while also feeding her solid food? And does feeding her solid food invalidate the suckling, so it would not count among the five full sucklings?

The suckling that prohibits marriage consists of five known sucklings within the two years (of infancy). A suckling is defined, according to common practice, as the child being breastfed and then voluntarily stopping drinking. It does not matter if the child ate food before suckling, nor if he became independent of milk due to food, as long as the suckling occurs within the two years. This is the view of the majority of jurists, in contrast to the Maliki school.