Welcome to the forum, hms_dubai!
17C isn't too bad (I would love to have that here right now, it's -14 and going down to -25), but I think it's a little too cool to keep a young puppy outside. I would also be concerned about having the little one accidentally getting through an opening, or jumping or the railing, and getting hurt. JRT's are able to jump to quite a height, and are very energetic. You might want to put Lassie's bed or box next to the balcony door and keep the screen open a bit if you are wanting her to get some fresh air at night.
About the dog food, if you have a pet store there that also sells food, write down the names of the food they sell, and post them here under the forum for dog foods, and I'm sure you'll get some responses as to what would be best for her. You could also start her on a raw diet. There's a lot of good info in the dog food forum, recipes, different feeding styles, etc.
It would be nice to see some pictures of Lassie.
There's a forum for that too!
Peepmouse, Mom to:
Cinder (11) Beagle/Corgi x
Maddie (2) Boxer/?? x
Pepper (16) Border Collie/Blue Heeler x
Samantha (15) English Springer Spaniel
Saving just one animal won't change the world, but the world will change for that animal.
The soul is the same in all living creatures, even if the body is different.