We're trying our best not to enforce hard limits if possible, so as not to stifle people's creativity and fun! We are, however, asking that you be reasonable about it — if she's summoning several at once, that's going to be a bigger drain than calling up just one, and the more complicated they are, the more taxing that'll be, and the longer she goes on trying, the harder it'll get, etc.

If you really want an upper limit for reference, we can definitely pick an arbitrary number for you to use as a guideline, but otherwise, just use your best judgment.