This is a great question, but does not have a pat answer in terms of quantity.
However, let's take a look at the answer in terms of quality-- quality of the balance in your daughter's life. Each child is unique and will handle the pressure or stress of extra curricular activities in individual ways. From your description, I would say that at this time your daughter appears to be managing both her academic and non-academic activities comfortably.

You have done a great job in examining several key factors that can inform you as a parent. You have assessed her homework completion, current learning capacity, health effects, irritability, and complaining. In the interest of balance, I would encourage you to also assess the time she has available to be quiet, to play, to be with friends in unstructured situations, and to spend quality time with you and other family members.

Your daughter sounds like an active and interested-in-life youngster.  How terrific. However, if your intuition is telling you that adding more to her plate might tip the scale, listen. Parent intuition never goes out of fashion! If you decide to limit the activities and she is disappointed, you can point out that there will be times in the future to do the other things that  she is drawn to doing. You might even make a long-term plan for how to build in her other interests.

In summary, use what you know about your child's personality, and the way she is handling her current extra-curricular schedule. Continue to assess other needs she may have, such as need for quiet/down time, family time, play time etc.  Add your intuitive wisdom to the mix, and you will be on your way to knowing what is a reasonable amount of time for your 7 yr old daughter to spend each week doing non-academic activities.

Bette J. Freedson, LICSW, LCSW, CGP

Sounds like you are all very busy.  That is a lot of extra "running" to do, I'm surprised Mom & Dad are not tired.  I think it's great that you've allowed your daughter so many opportunities and I'm certain that this has not effected her negatively or she would not want to continue to add even more.  However, I think that there should be a limit and I believe you have reached it.  It looks like the acting classes will end shortly and maybe then you can add something to replace it, that's the good thing about these 3 month activities, they end soon enough to change to something else unlike the classes that continue year round.  Have fun with your social butterfly!  Best wishes!