Surely Grindlewald would find Queenie to be more trouble than she's worth?
Because he suckered her in by letting her think that he'll support her desire to marry a muggle, when he actually wants to slaughter and subjugate muggles... and she can read minds.
Okay, in the later Potter books it was established that a few wizards could read minds, but only the best, bravest, and most disciplined could maintain a false front around those who could read THEIR minds. So maybe Grindlewald could fool a mind-reader into thinking he's not a wizard Nazi, if he minimizes contact with him.
But how could he prevent her from coming into contact with all his team members who are looking forward to the coming muggle slaughter? How is this not a massive plot hole?