It's totally normal for sleep patterns to vary and for young children, in general, to need a parent's help to sleep at least some of the time. Just because they sleep well at one point, doesn't mean they always will, and vice versa. On the whole, it gets easier as they get older.
Babies feed for all sorts of reasons, not just nutrition, BUT that doesn't mean they don't need it. There's no need to let her cry - meet her needs and in time this will pass.