It's an opinion and as about valid as any other....
But he’s still her Grandson and although her heart may very well be breaking for both him and the institutions she holds dear, she will feel that she must support him as a Grandson first and foremost until he, and no one else, calls time on it.
Just my opinion.
Though you'll agree it's based more on guesswork than fact, right ?
She may well take that course, I'm not sufficiently close to her to know, but going purely on how she has served the country, Empire, Commonwealth and all their peoples for the last sixty-eight years, she might instead take the view that while he is her grandson, he is also a grown man and must stand up for himself and for his son.
While in that case she might also choose to assist them through intermediaries, her decision may be that on a scale of balances the interests of everyone else weigh more heavily than those of Harry and Archie.
I honestly don't know as Her Majesty has not made me privy to her thoughts on the matter.
And had she, I wouldn't be making them public.