VandT - I had this problem with my LO from about 8-11mo. He would wake anytime from 4.30-5.30am, drain a bottle of milk in about 2 mins and then go back to sleep again till about 7am. Although myself exhausted, it 'worked' for us until one day I had just had enough. A dear friend took the brave step (!) of being brutally honest and said that there was no way it was hunger, but at this age (11mo) it was habit. What baby/toddler would refuse to have a nice, warm bottle of milk with their mother in the early hours?!?!? She was right, and deep down I knew it! So I cut it out altogether and after 3 nights of a few tears (!!) and some early starts, he started sleeping till 6.30/7.15 and has done ever since. I swear he is happier cos he sleeps better and so do I!
What I am trying to say is, that from what you have said, it sounds like your mum is right! She probably is milk dependent (she only NEEDS 12oz a day). At 4am she is probably waking from hunger and from habit. By dramatically cutting down her daytime milk and refusing to give her milk at night, she would hopefully increase her solids and, at this age, it is solids that are going to keep her fuller for longer. Also, maybe give tea a little later?
If it helps, my 12 mo feeding is as follows:
7am: wake
8am: breakfast - cereal + fruit (+yoghurt sometimes) with 3-4oz milk.
10am: snack (only if he has had a small breakfast) - raisins
12pm: lunch (carbs, meat/fish, veg)
2.30pm: snack - raisins/biscuit/fruit
5pm: tea (same as lunch) with 2-3oz milk
Pudding: baby porridge mixed with custard (I am convinced that this is what keep him nice and full!)
7pm: 7oz bedtime milk (i.e. not cows, but a nighttime formula)
Water is offered throughout the day and with lunch.
I hope things start to settle down soon