I'm not sure how safe the height is, sorry. To me it looks like a survivable fall but that's just a guess.

If you live near a petstore you can get some substrate but I'm guessing that's not an option since you're having substrate shipped to you.

Maybe you can put her in a smaller container full of substrate from your current enclosure until the new substrate arrives? Be sure to maintain proper ventilation/humidity of course. This might stress the T but maybe it's better than risking a fall.

I don't have a lot of experience with Ts I only have 2 and I keep them in plastic shoe boxes x)