[EVERYTHING] Hang on a sec...

Why doesn't Dany just take her dragons north of the wall and eliminate the army of the dead by burning them? Quick and easy. Makes use of dragons who are otherwise flying around idle. Okay it doesn't take care of the white walkers but how many of them are there? Without their army they wouldn't be anywhere near as threatening - especially now that Jon has dragonglass.

Dany's pausing her entire invasion and claim to the throne because she believes the white walkers and the undead army exists. So she's decided to acquire proof to convince Cercei, thus forming a truce with literally the least trustworthy person in existence. Just use the dragons!