Daughter has constant runny nose and nighttime cough. she is four and had a cold weeks ago. could this be allergies?

Could be: How long have these symptoms been going on? Any changes at home? Any new pets? Any family hx of asthma or allergies?

Could be: this could be related to allergies, but also could be due to a few other conditions. She should be evaluated by pediatrician with a physical examination which can help to further suspect allergies with treatment and/or further evaluation as needed.