People with this kind of heart, this openness to experiencing joy, are like unicorns, and you're lucky to have one in your family.
This may sound absurd but I recently watched the comedy show "Baskets". The best part of that show is the late Louie Anderson's portrayal of Christine Baskets - a character he modeled on his mother.
Christine sees the joy in nearly everything. She orders room service from a hotel room and thanks the employee by name. I know it's just a show but the realistic portrayal of someone seeing - and contributing to - the good things in this world revealed to me how, quite often, my first reactions come from someplace sour and snide. Why?
I'm making it my mission to be more positive and I love these observations you've made about the example L sets for you.