How can I help my baby with her cough?

My poor 10 month old has had a cough for about 4 weeks now. We've taken her to the GP who said it was viral (she is newly in nursery) so not concerned there, but it's just horrible hearing her cough so much especially when it disturbs her sleep. We already run a cool mist humidifier at night and sprinkle her sheets with baby Olbas - does anyone have any other tips which helped their LO?