Like loocyloo has outlined, a child’s experience will influence how they play and interact.
I think it is our role as Early Years practitioners/ childminders to play with the children and show them how fun things can be. Getting the activities to match the child’s interest plays a big part in a child being absorbed and independent in their play.
The expectations, accompanied by routine helps too.
The visual timetable is a great asset, the children can see when snack is and, as long as they are not genuinely hungry learn to stop asking for food at other times. I think you are doing the right thing in ignoring the food requests, as long as you know she has eaten at the last meal.
I was quite lucky in that I started every day with breakfast with all my LO’s so I knew what they had eaten, how much they ate etc... It was a lovely calm start to the day, we planned our day together and I could give the ‘you’ll be hungry later ‘ talk to those not interested in breakfast occasions. Grazing was not part of our day, just set times for meals and snacks and those who arrived as grazers soon stopped as they got used to our routine and absorbed in activities.
As the oldest she may like to take on the role her big sister does with the others, spending time with her planning activities she can lead might help.
Some children however are happiest flitting from one thing to another, prioritise the getting rid of food requests, have lots open ended activities that she is a little interested in, child choice set up where she can collect and return what she wants to play with, play with her one to one periodically if you can, to encourage her to stay longer on tasks.

It all sounds much easier when you are advising though...I can imagine it is quite wearing, you may need to plan time out for yourself from her too....a table activity, she joins or doesn’t, but you can’t give her attention unless she is at the activity? I had an older child who preferred to interact with me all day. When the LO’s were having their nap I would make myself a cup of coffee and sit and start writing the diaries, this child knew that I needed time out to do this and soon got in to the routine of playing with items from her quiet time box next to me, but on her own, not requesting interaction. Eventually a ten minute session grew to the whole hour of her absorbed in her play....and then it was the opposite way round...I wanted to play with her after my 10 minute diary writing!