She will always need to give you 5 apples. You both need at least 5 apples to begin with, but apart from that it doesn’t matter exactly how many you each have. When she gives you 5 you will have 10 more than her because she will lose 5 and you will gain 5, resulting in a net difference of 10.
For example, if you each have 25 apples and she gives you 5 of hers, she will be left with 20 and you will now have 30, precisely 10 more than she has.
Two of your neighbors were arguing about if the first man’s peacock laid an egg in the seconds man’s garden, who would own the egg. They asked you to solve their dilemma. What would you tell them?
Water. As ice I’m hard and cold, as water vapor I’m hard to hold and I’m always present in the air as humidity (aka water vapor). If the earth ever runs out of water, we’re toast.