Phlegm in throat - singers

Any advice/suggestions please for the that phlegm in throat sensation that makes you want to clear your throat (in the middle of a song!) for singers? 

My daughter is suffering bad allergies (time of the year) and gets congested and hay fever symptoms and gets this thing in her throat - she feels there is something stuck there and it affects her vocals and she's always doing that little "hem" cough thing...

Nothing from the chemist has helped... I plan to take her to a naturopath next but thought I'd check if others have this problem and have found a cure...

thanks!