Blankmonjay:
Many thanks for digging out that data. With 2016 high attainer P8 around zero and A8 of 64, it seems to me that the comp is OK but not particularly good in terms of high attainers achieving their potential. (2017 overall P8 is of course also worth including in your view on this). FYI, I am not claiming any particular expert status here, just an interested obsessed and geeky parent...
It is not fair to expect your comp to be on par with the grammars (which should look better, as their intake were selected via additional tests, so presumably an even higher-attaining subgroup of the high attainers), but you may want to compare your comp to other comps in your area, even if there is no way your DD will go there, just to help you gauge your own comp's performance. But therefore let me also say that if the (high ability) A8 of 61 for Grammar A is correct, it hardly seems worth travelling to, compared with your comp! (But if its overall A8 in 2017 is strong, perhaps 2016 was a blip or some measurement or transition issue (e.g. did not fill all 8 buckets, or similar explanation).
I did a quick check of our local comps here (in London - so may be quite different from your area), and the four schools we are keen on have (rounded) 2016 high attainer A8 of 66, 68, 68 and 69 - all with positive P8 overall 2016+2017 and high attainer 2016. Two of these are very oversubscribed with all kinds of hurdles, and two just about fill their spaces, three are Ofsted Outstanding, one Good. Four other local schools that we will not put on our CAF form (for a variety of reasons) have 2016 high attainer A8 of 60, 62, 63 and 65.
Not sure this made anything easier for you, sorry...
Grammar B has a really quite bad commute, but may also perhaps be the best fit for her, ignoring the commute for a moment - especially since you mention that she enjoyed the work, the comp's lack of setting and some disruptive behaviour etc. Also perhaps consider her personality - would be stimulated (or feel dejected?) by academic competition and (perhaps) being middle of the pack at the grammar? Or would she be spurred on (or slack off?) by being near the top of the comp?
One thing is certain, though: If she is going to be slogging her way to and from the grammar every day for years, she needs to own that decision!