Teaching a 7YO About Waste

You can could try a fieldtrip to the dumps and recycling plant. Also if her favorite rock star or movie star has gone "green" then you could lure her in that way.
It is hard for a young child to comprehend their impact on others. I remember my mom constantly conserving water and food when we were young adn I thought it was dorky, but now I know how to conserve as an adult.
You could also try "competing" with her to see who can make the toothpaste last longest? The winner gets to pick a family destination...You can also start by giving her her own bags for shopping.
Conservation must be taught, but I think the lesson can be fun.

My mom taught us how to portion things by using sizes of things to compare to. Such as when using shampoo or conditioner, it should be the size of a quarter in your hand. toothpaste should be the size of a pea. dish soap about a teaspoon.

Another thing, there is hair detangler in a spray bottle, just say use 3 or 4 sprays instead of giving her one she can pour out.

Funny thing is, I am 36 years old and still use those measurements, lol.

I would try putting such items into travel size bottles. One travel size bottle of each thing should last for a week. Give her those bottles and tell her they absolutely have to last the whole week. If she runs out, then she'll have to wait till the next week to have more. This should show her how to ration and use less. Since is such a small bottle it should be relative to her attention span at 7 y/o. Good luck.

watch them every second and tell them how much befor they even start to use something when they start crying about you doing this then tell them when they can use the right amount the right way then you will stop till then tough

good luck

You might try working out an allowance for her for these kinds of products. Figure out how much she should be using in a week or a month, and how much it would cost. Then give her that amount to purchase her own hair products, soap, whatever it is that you want to work on, that will be for her own use. When they run out before the next allowance time, and she doesn't have the money to replace them, she'll learn to portion it out better. And if she learns to be frugal about it, she might end up with a little extra spending money for herself. This idea might not quite work if you only have her one weekend a month, but you might find a way to adjust it to fit your situation. In any case, find out what would really motivate your girl and use that to set up a plan of attack. (My kids are highly motivated by money.) Hope you find something that works.