I find it barbaric that you have friends who have done CC with babies who are weeks old. Even if it 'works' now (ie they've successfully taught their baby that there is no point in crying because no one responds - the definition of neglect, basically), there is absolutely no guarantee that they'll still be doing it at three months, nine months or even three years.
Sleep is developmental. Some babies are able to sleep independently and with minimal support from weeks old. This is not a sign of a 'good' baby or brilliant parenting skills, it's just normal for that baby. Some babies are unable to sleep independently, or remain asleep for long stretches, until well past a year old. This is not a sign of a 'bad' baby or terrible parenting skills, it's just normal for that baby. In the end, they all eventually sleep.
I had both of my DSs in bedtime routines from days/weeks old. I was breastfeeding and shattered from hourly night wakings so hadn't the least desire to stay downstairs and watch TV, so I went to bed when they did around 7ish, with them in the same room as me. It really made no significant difference to their overall picture of sleep (highly dependent sleepers with frequent night wakings for 18mo-2yo each). I suppose the only difference it made was it eased the witching hour shrieks. As soon as I did bath, pyjamas, dim lights, boob, they calmed right down. It may possibly have cued 'night sleep' versus 'day sleep' for them as well as their night wakings, though frequent, were never lengthy the way reverse-cycling babies tend to be. But I am entirely willing to accept I got lucky in that regard I must have got lucky with something with the amount of sleep those little buggers robbed from me
When you say she won't settle with you downstairs...are you trying to put her down? Will she fall asleep on you then wakes when you try and put her in a Moses basket or peak? If so, the easy answer is: don't put her down. It's fine to let her sleep on you if that's how she sleeps best. She won't develop bad habits.