Hi TeaOneSugar:
DD1 currently in Year 7 and we were in much the same boat. She desperately wanted to get into two grammar schools but only scored high enough for a third, quite a distance away. She dreaded the long bus journey on her own so opted for local (and very good reputationally) senior school here, which is only a short walk away.
Things that helped:
We reminded her that a few of her friends (not best friends, but good friends) were also going.
We attended the welcome meeting. It was actually less crowded then the open day before we applied - and I think walking around and talking to people helped her feel a bit more comfortable with the prospect of going there.
The school held a transition day toward the end of Year 6 and this made a big difference. She met a few people who seemed very nice, liked her tutor group, the school had lots of nice activities on which she enjoyed and by the end of the day she really was quite chipper about going there.
She liked the uniform and buying 'the kit', letting her choose the 'cool' shoes rather than practical shoes and a ruck sack all helped make her a bit excited about starting a new school.
Six months into Year 7 DD1 adores her new school. She's realised that not having 1.5 to 2 hours of homework a night (typical workload for a King Edward Grammar here in Birmingham by all accounts) means she has time for her sport and music interests (which are important to her) and can easily manage the homework which does come home (more like 30 to 45 minutes a night/ more at weekends - about 1-2 hours at weekends). She also has plenty of time to read for pleasure - and indeed is currently devouring library books (school & local library).
So although I personally was a little blue that she hadn't made it into a grammar and do at times worry a little about the lack of homework compared to what grammar school friends report their children are doing - I have a very happy kid, who's doing well at the school, seems to be really enjoying her academic success and has all sorts of time for clubs/ sports/ music - all of which she thoroughly enjoys.
There was an advice on Year 7 feed last year: www.mumsnet.com/Talk/secondary/a2130278-Advice-for-starting-in-year-7 which had a lot of useful advice; much of which still holds true.
Finally - assure your DD that you will keep her on the waiting list for her first choice school. Find out how that works. Here the city council keeps you there until Christmas - After christmas you have to approach individual schools and request that you are added to their waiting list.
I asked DD1 if she wanted me to contact the grammar schools (she just narrowly missed the cut off) and keep on their waiting list in early December and she said 'No Mum, I'm really happy and want to stay where I am'. Personally I think there's a lot to be said for being a big fish in a small pond. At her present state comprehensive she's seen as bright, teachers are noticing her for the right reasons and she's clearly doing very well. Hand on heart - I'm not sure that would have been the case had she gone to a grammar school - and that dent in confidence may have disuaded her from her interests in maths/ science - both of which she's mad about (recording hours of science/ maths documentaries I get roped into watching with her - Fortunately I find Brian Cox fairly dishy so I don't tend to mind).
HTH