If you need to think of Donna's singing voice, think of Laura Bailey's voice. Basically the Boss from Saints Row the Third onwards and Lucina from Fire Emblem Awakening. Personally I see her singing love ballads and some songs in German, Arabic or even Russian.

https://www.youtube.com/watch?v=jN0HaewWh4g

The Instructor doesn't drink but he'll watch out for Donna in case she gets too drunk and flirt with someone.

Another fun fact: Donna's Christian so religion can make a good conversation with Captain Mask.