It's a good idea to hold off on solids (including rice cereal) 'til at least 6 months to decrease the chance of your daughter having allergies.
How often does she eat? My 5 month old DS eats about every 2-3 hours during the day (I'm not sure how much as we don't usually bottle-feed... on the occasions that he has taken a bottle he's had about 3 oz for a feed) and usually gets up once in the night and once early in the morning. And I'm ecstatic about that since my DS1 used to get up 5-6 times a night at LEAST.
Keep in mind that all those people you hear saying that their babies sleep through the night are only talking about a single stretch of 5-6 hours. Your DD is probably already doing that.
As long as she's growing well and has good energy and seems to get full & happy... I wouldn't worry about it. She really will sleep through the whole night eventually. ;)