Routine sounds good, So I'd say it is just that she is hungry & possibly that she just doesn't need as long a sleep over night... my ds#2 (almost 7mo) cut back from 12 hours to about 11 hours around 4.5mo (with 1-2 night feeds)
It is actually very normal for most bf babies to want 1-2 feeds at night up until about 9mo, so the fact you have had her sleeping throught the night is great, but it doesn't surprise me now she is a bit older & life is more stimulating & she is using her muscles more, that she needs the extra feed, or can't last as long between feeds...that is the thing about babies, once you think you have it worked out, they develop & it all changes.