Please refrain from using fractions on public forums as it may be taken as a micro-aggression towards some European members who rely solely on the metric system. As a side note, three-quarters of Americans don't understand fractions, and the other half don't even care.
เป็นลูกไหม sounds more like, "Is it a child?", or "Are there children?". However, ลูก is also a classifier for round fruits, round objects, storms, etc.. Was there anything else in the context of the conversation that she might be referring to?