The grey t-shirt turned out the best. I used one of K's t-shirts and retained the existing neckline and shoulder seams, but cut out all the rest using one of R's tops as a guide. I also used the sleeve hems to be the hems of the flutter sleeves, which worked out great.
The bluey-grey t-shirt is not upcycled. It's made from some stretchy cotton jersey, with the flutter sleeves made from South African Three Cats fabric. I got lazy and didn't use my double needle for the hem; consequently it doesn't look great. Oh well...
T-shirt number three is made from an old top of mine and I have no idea how it looks on R because I haven't yet tried it on her and she was too hot and bothered after school to model anything (and I was too hot and bothered to take decent photos). I'm thinking the sleeves look kind of ridiculous - I didn't have much fabric to work with as I had to avoid a paint stain on the original top - but if they look silly on, I'll just downcycle it into a rag and call it a learning experience.
In my enthusiasm for upcyling I made a little stamp with a recycling symbol on it, so my upcycled garments now have their own special label!