it could be the cordial, it has alot of sugar in it, having it in a bottle is also bad for her teeth, I'm not trying to sound judgemental or anything but maybe you could try giving water in the bottle and offer juice in a cup but not as often and make sure she eats healthy food (which I'm sure you do anyway).
We go to music and movement, not sure if you have it over there but its great to get the littilies dancing and moving. If shes fairly active thats a good sign that she is pretty healthy, its when they get lethargic and out of breath often that you need to worry but maybe you need to see a doctor incase its something else medicaly thats making her put on weight.
hope all is well and keep us informed.
2 little darlings 29/01/03 + 17/03/05