Here is a link that might reassure you:
http://babywhispererforums.com/index.php?topic=85130.04-6 months
4-6 months Two naps, 2-3 hours each OR;
Gaining mobility 3 naps; 2 2hr naps & 1 45min catnap
10-12 hours at night
So given that she is 5 months and not willing to take a CN, you are looking at 2 solid naps between 2-3 hours. Given her age and high sleep needs she just isn't ready for longer A times to NOT beable to cope without these longer naps IYSWIM? And at least that way it gets you through the day to not too early a bedtime.
So let her nap while trying to push out those A times a bit.
So maybe something like:
6.30 Wake up and milk feed
8.15/8.30am Nap
10.45/11 Wake up and milk feed
2.25 A time
1/1.15 Nap (for 2.5 hours)
3.30/4 Wake up and milk feed
2.25 A time
5.45/6.15 milk feed and bedtime
Something like that? 5/5.5 hours daytime sleep is probably going to be ok without affecting night sleep. Once you are sure OT is gone you can push the A time more if you feel she is ready for it.
4 milk feeds (or 3 and a half) is fairly normal for this age. Does she take full feeds? Have plenty wet and dirty nappies? She really does love her sleep!!
What do you think?