I think that by the end of the year -- when there is a very good chance we will meet Baylor in the FF -- the answer is
yes.
Not because Breanna or anyone else in WCBB will be capable of defending Griner straight up with no help, but because Breanna has a combination of length and athleticism that will allow her to
be the help, and a very effective one at that.
Breanna has such a crazy vertical and crazy quickness for one of her wingspan that she can sag off other players and still close out on them, at least the ones she's likely to guard (or in a zone). From many positions on the court, this will allow her to disrupt a fair % of entry passes to BG and to quickly be in a position to double BG or help on her, or simply occupy the middle of the lane should BG turn to the middle. (When BG is allowed to turn baseline, that jumper is nigh on impossible to stop.) Breanna's skillset would mostly be wasted if she played
behind Griner. Stef and Heather are better suited for that role.
Furthermore:
I know everyone says there is nobody in WCBB who should really be trying to block or harass BG's shot because they'll just get her on the elbow. This year, I agree. However, I think that in most cases BG does not jump very high on her jumper (why bother when you're 6'8"?!?!), and that next year there will be
one player in all of WCBB who--
as a help defender--could keep BG honest. That player is Breanna Stewart. She is that special. I still wouldn't recommend trying to block BG's shot from straight on, because BG holds the ball way back on her jumper. This is why I stress the point of 'help defender'. Help defenders have space, and angle.