I'll have to think about this one.
Is it really the situation she was in? And even if it was, wasn't she to blame (with her inconsistent policy and possible involvement in botched assassination attempt) for things having escalated to such a fever pitch?
Is it really the situation she was in? I don't know. I haven't read Starkey on the issue, so I'm not sure what evidence he found of a plot by Coligny, but while Starkey isn't perfect and occasionally irks me, he's generally a VERY reputable historian. That at least gives me pause and makes me desperate to read his work on the subject and view his evidence.
Did she believe that's the situation she was in? Again, I don't know, but she could either stand by her son, or lose her family when the public outcry arose and the Protestants took retribution. Because this WAS a time of retribution. Both sides butchered each other, and there was already a lot of talk against the Royal Family for the attempted assassination of Coligny. I think what matters most is whether Catherine FELT that was her choice, her family or innocent people. If to her, that was the choice, that's how she should be judged, on her own perception of the situation. Why do we read as many books as we can find on a given subject? Each author has his/her own bias, and reading several opinions gives us the most balance. It's the same when looking at a person's reaction to a situation. Some say Catherine had no choice, some say she was cold-bloodedly responsible for what happened, I say there was an in-between, that she chose her children over people she didn't know. A choice, yes, but it seems a fairly natural one, and I don't presume to judge.
The botched assassination attempt...yeah, I'd say that was her fault, but also the fault of Maurevel, the assassin, and de Guise. Catherine did what she could to stop the damage, going and visiting Coligny along with the king, and as for her 'inconsistent' policy, it was generally that of making peace between the two sides, but a few times, she just didn't THINK. Like going to visit Élisabeth/Isabel at the Spanish border. To me, that's the act of a mother who wants desperately to see her daughter and doesn't think of anything else. Then, she comes home and gets the backlash. Felipe was urging her to root out Protestantism, she refused. She went for tolerance before violence. Then, the massacre happened. Her efforts didn't stop in 1572, either. She kept trying for peace, she kept advocating tolerance, and she kept forgiving her children whatever their betrayals. I say to even START to judge Catherine, we have to look at her entire life and what she did from her husband's death until her own as the force behind the throne.
As usual, just my tuppence. Awesome questions, though, bell_the_cat. Archibald Douglas was an interesting character himself, so I love your username.

Regards,
Arianwen