are there any fallacies?

But pop quizzes do make sense. Whether it causes more work for the professor should be of no concern of the student. Unnanounced quizzes makes students nervous only if they are not keeping up with their work . She claims that students keep up with their work so pop quizzes are unnecessary because they are all motivated to keep up. This being the case pop quizzes prove the student right or wrong. Furthermore pop quizzes have a practical value from the professors perspective. She is wrong. None of what she says makes any sense to me.

I like Trevor's re-statement as premises and conclusion.  It helps make more obvious the elements of the discussion.

In addition to the premises he provides, there's at least one other implied premise that is missing from the list but probably in plan behind Adam's niece's reasoning ... that premise would be that there are only 3 criteria determining whether pop quizzes are good (or that the 3 premises provided represent an exhaustive list) ... work for teachers, student nervousness, and student motivation.  If these were the only 3 criteria (the implied premise I mentioned), then the logic would flow ... except that I would suggest that the implied premise I added is false.

And, in the false premise department, I see Trevor's revision to "Students do not need ..." as helping the argument by changing P3 from a value statement.  From the perspective of the overall argument, this revised statement would seem to be a false premise.

I see fewer issues with Adam's niece's logic and more issues with the validity of some of the assumptions she's making.

You draw attention, Arlo, to an important distinction,

The soundness of the premisses as distinct from the validity of the logic

I think the validity of the logic is evident when we replace 'should' with 'is' and abstract the assumptions:
[I've included your helpful addition]

A causes B and B is undesireable
A causes C and C is undesireable
A is unnecessary
There is no further relevant information
Therefore - A is undesireable

The logic is entirely valid. Based on this information alone, it is hard to conclude anything other than A is undesireable.

As you point out, however, the assumptions are just that.

So the rule modus ponens can be applied.

If P then Q [If the assumptions are true then the conclusion is true]
P [the assumptions are true]
Therefore Q [the conclusion is true]

But - it's a big if.

NB.
If the premisses are unsound, in that they are not true, we need to be careful not to fall into the trap of denying the antecedent. Even if her premisses are untrue, Adam's niece might be right that it doesn't make sense to give a class pop quizzes - just not for the reasons she gave.

Maybe cherry picking (if pros are ignored intentionally).