Inappropriate or not

My SO cares for his mother with mental health issues at the moment so we both live with her. She asked us if we're practicing safe sex because she wouldn't want me getting pregnant by accident. Is this inappropiate for her to ask? Considering we're both adults and can make our own decisions. Or is it appropriate for her to ask? 
I don't know what to think, which is why I'm asking for opinions. We kinda just stood there feeling kinda awkward because she's asking about our sex life.