Similar to what others have said, really - it can be pretty hard to get a sleep routine at that age, but don't despair - it doesn't mean they'll never sleep well. From about 3 months I found it quite easy to get DS to go down for a nap, but he would wake up without fail after about 20-30 minutes, and wouldn't go back to sleep. Then, suddenly, around 7-8 months, he just started staying asleep for longer - and in the space of a fortnight or so, he was sleeping for 2 hours every lunchtime, plus an hour in the morning and afternoon (can't quite remember when he dropped the afternoon nap).
So, even though I know how frustrating it is not to have a daytime routine, sometimes it just can't be helped. Everyone's different, but I personally don't think it's worth the trauma of leaving them to cry themselves to sleep to see if that works. Small sample, I know, but those mums I know who have tried controlled crying still have children who don't sleep well at all. I never left DS to cry - he just learned how to sleep without help, when he was ready.
Having said that, I do think your DD is getting to the age now where a bedtime routine is worth starting - so that when she learns to sleep in the day, she's already got some sort of framework. Just start doing bath, book and bed (putting her down upstairs, not downstairs with you) at around the time you'd eventually like her to go to bed - even if she's still up and down again after 'bedtime' at the moment.
Good luck - and as someone else said, try not to put too much pressure on yourself or her - she's still very little.