Steam...
Water Vapor is Steam... Steam has a smell... I swear it smells like a dry Cleaners.. Also, i just had a leak with my chevy,, the water pump was shot, during the couple weeks of finding that out that was the problem which i did get fixed, That smell which was the steam from the water leaking, not the antifreeze, but the water itself evaporating is what I know your mom is talking about. A humid morning has the smell. boiling tea kettle.. just walk near it.. Just my take on that..