Just a guess but she probably would have taken the buss back if you weren't there? Like, she wouldn't want to bore you waiting for the buss or try to time it shopping with a kid.
I think it was the weight of the shopping. My food would have increased what needed to be carried, but I was too young to be much use carrying it.
The point is taxis supplement and can replace public transport for low-income or unable-to-drive people in some situations — not necessarily every day.
