I think all the stuff David Allen said about "Waiting-for's" applies to delegation.

I don't understand what you mean by "control". I wonder whether you've
defined what your assistant's responsibilities are precisely enough and whether
you and she both have the same ideas about what they are.

Maybe "control" just means "maintain a list of".

As I see it, for each task there are three people responsible: the person
whose job it is to do the task. Your assistant -- what should she do?
Check to see whether the task is done? And ultimately you -- you're
responsible for checking that the tasks are done, even if your method
is just to ask your assistant "Did all those tasks get done?" and check
that her answer is "Yes".

You may also need to communicate the priority levels of the tasks.
If one of your workers is busy with other things, they might not find
time to do something unless you make it clear that it takes a higher
priority than the other things. You might need to provide your
workers with clear instructions and the things they need to get the
job done.

How do you check whether the instructions were understood well enough?
How do you check whether the way the job was actually done (which
might not have been predictable in detail by anybody in advance) is adequate
for the purpose?

Maybe the workers need to be asked from time to time when they expect
to complete a task, how they're planning to do it and whether they have
everything they need.

What exactly do you want your assistant to do? What exactly do you yourself need
to do next about all this, and when? (E.g. wait a week and then ask your
assistant how many of the tasks are complete.)