Hi Lotte
Sorry to hear that you're having problems.
I completely understand how tough it can be when they don't sleep through, especially after being good sleepers before.
How old is your DD now?
Is she still only 6 months?
If so, it's quite early to be on 3 meals a day.
Many people start on one and gradually build up to 3 by about 9 months.
She's eating happily, which is great, but how does her body seem to be coping? Is she filling nappies regualarly and without any problems?
One big possiblity is that the waking is not related to the eating.
It's quite possible that the timing is merely concidental.
Many babies start waking at night at around 6 months because of teething etc.
Is there any chance that this is the reason in your DD's case?
Also, is she starting to crawl etc now?
If so, it could be that she is very hungry due to the extra physical activity.
Whatever the reason, you will probably find that it is just a phase.
All babies go through them. Those that slept well before start waking and those that used to be awake all night suddenly start sleeping through.
There's not much you can do except wait for the phase to pass, safe in the knowledge that she will start sleeping better again soon.
Sorry not to have more practical advice.
Maybe someone else will come along with something better to offer...