Um - does your SD live with you full time, and do you get the Child Benefit for your SD? If you do, then personally I would go round both schools - not just on their open evenings (pupils at open evenings are cherry picked form the BEST behaving / highest acheiving in the school), but also arrange to visit while lessons are on. This will give you a much better 'feel' for the school, and a much better chance of seeing which one will fit your SD's personality and interests best (also ask about after-school activities).
However, if you are not in receipt of the Child Benefit and your SD does not live with you full time, than all you can do is what I've mentioned above and tell the main carer what your opinion is - because even in cases of 50-50 shared care, one parent is still in receipt of the Child benefit, and it is THIS parent that legally MUST fill in the application form, from THEIR address. Otherwise it is fraud.
Also, either way, if you want your SD in the Grammar school - I would start prep work NOW (my DS1 is in Y5 and hopefully going to do his 11+ and get into my local Grammar School). Find out what the 11+ involves in your area (each is different), and get some work books going with your SD - or get a tutor if you can afford it. There are some good tips on Eleven plus forum.
Getting into Grammar school is not done in the same way as applying to your local catchment Secondary school - you have to ASK the school for a form for the 11+ exam, and pass the 11+ exam AND be in the top X amount (varies by the intake amount for THAT Grammar school) of the people applying for that school - but you STILL have to put that school on your ordinary application for Secondary school form from your LEA as your first choice.
So YABU to think that getting into Grammar school is as easy as writing that school's name on your SD's Secondary application form. YANBU for giving serious consideration in Y5 to Secondary choices. YABU to not say in your OP if your SD lives with you FT or not (makes a difference to how much 'say' you get in the Secondary application process).
My thoughts - unless your SD is currently working at NC Level 4a or Level 5 at the start of Y5, she is unlikely to pass the 11+ with a high enough mark to get into Grammar school (at least in my area, don't know about others), only you will know if this is the case. If your SD is not working at this sort of level now, I would ponder whether the Grammar school will be the right environment for your SD to flourish.