It has long been an old wives tale that a hot toddy (hot whiskey) is a good way to relieve the symptoms of the cold and flu. Well it turns out that there actually might be some merit in this argument.
Apparently the heat is beneficial to clearing up the dreaded nasal congestion, whilst the whiskey also helps the situation. When we drink alcohol, one of the side effects is the dilution of blood vessels. This dilution then assists the membranes in their fight against infection. So it seems like your mother may have been right all along.