How do you know she's not having enough? It can be hard to tell how much abreastfed baby is drinking. Do you have a baby scale that can detect before and after feed weight, sensitive to measure a change of a few oz?
Anyway, given that you are worried I would recommend you take your baby for check up asap. Concerning is the fact she's sleeping more than usual. Maybe she caught something. Even without fever change in behaviours, particularly level of alertness is a concern. Does she have rash? Is she having less wet nappies than usual?
That said, it could be nothing wrong and just her adjusting to being home from the trip. However babies at 4 months may start drinking more, but less frequently. They also become more efficient at drinking and can finish more quickly.
But better safe than sorry. please see Dr. In meantime keep her cool and keep offering her a drink every 2 hours.
Has there been a change in bowel habits or how many wet diapers she's producing? It's my understanding in breast fed babies b/c we don't know how much they're consuming unless theyu're weighed before/after checking diapers is the best way to tell if things are okay. Maybe she's teething...?
I agree about checking the diaper. Regular urine is usually a good sign. We just gor back from a trip to england with our 8month old and she did initially decrease her feeds and sleep a lot more. From what I gather this behaviour is completely normal. Especially while they are trying to regulate their body clock.
As long as you are feeding her on demand, whenever she wants to feed she sounds like she is doing fine. I also found around this age they become far more competent feeders so, while you may think she is not consuming a lot, she may be getting quite a substantial amount.