These are lovely and your sister is a gorgeous subject :D

First tip I can give you that will massively improve your portraits instantly and is the easiest one as well: look back to the shots above and count how many have cut off limbs and/or fingers and in which shots a 'zoom out' 'steep back' of a few centimeters would have prevented that! :-) Cut off limbs and fingers are something people overlook easily since we want to capture that smile or look, but also the first thing we can improve on.

Cheers, and great to see you experiment, it's such wealth to have great shots of the people we love :-)