She has cried in public, a few years ago apparently she got choked up at a WWII memorial service. I've never seen the footage to prove it but she did apparently get a bit sniffy, not sobbing mind you, but a bit misty eyed and I've seen footage where she got visibly emotional when the royal yacht Britannia was being retired. I don't think her reserve it all due to her being the Queen, many people of the WWII generation don't wail and sob over everything.