What a great story. I love that this is told entirely from Shelby's point of view. Prevents the wildly inaccurate descriptions of physics and how things look from such a small perspective. Also, her inner thoughts as she's playing with Gus lend some level of rationality and logic to her physical actions.

I hope that if you do continue this story in a sequel, you keep it from Shelby's point of view.

This was all very high quality, grammar and flow is smooth, conversations work, is all excellent. 

Fo a squeal.. well theres always hopeing for more tinies to be found by the two, tiny women too, exploring more ideas from the giantess and shrinking community, just their conversations of their opinions on this stuff might be interesting. More personal one, and probably said way too many times to other authors, is wedge heels. Once could be made with a little compartment to store and hide tinies in, and for giantesses that crush cities, the large surface aria allows for maximum crushing besides also making it more stable. Wedge are aperently better then most other high heels. 

You’ve got some skill and a good start, eager to see what else you can wordsmith!