Hi, I've read bits and pieces from your thread and it seems like you are doing a lot of the right things and you need to carry on with this. Well done for all the hard work you've put in!
I agree that portion sizes and upping activity will help, but you also want to ensure she is satisfied after each meal or she will look for snacks that may be unhealthy.
Protein, veg and good fats are your friends here. Sugar and refined carbs are not! and whilst I don't think you need to get into calorie counting/weighing out portions continuously, looking at the overall days intake will help.
Be careful with things like Ready Brek as it's highly processed. Porridge oats (rolled or whole) are s better option. Most yoghurts have a huge amount of sugar in too, so watch that. A good Greek yoghurt, even if full fat, would be better.
Switch to brown rice, brown bread, brown pasta if you haven't already done so.
Aim for 50% of plates to be veg. There are lots of interesting recipes on the internet to make this a bit less boring. Too much fruit (because of the sugar) isn't a good idea. Also fruit juices and smoothies, although they look healthy, should be avoided.
Yes to drinking lots of water too!
If you keep doing all this and continuing with a lot of activity her metabolism will go up and she will lose weight. Slow loss is good loss!