Seems like it'd be perfectly secure.
I just wanted to add that I think it's important to start a puppy young outside/etc, if you don't - they may never learn to have positive experiences with it. Basically I don't think shielding them from stuff helps anything (I noticed how you said she's too small to go on walks, and I think in another thread, you also said you did not want her going outside).
I always let Jackson go and explore, encouraged him to investigate new things, build confidence, etc. He's a bigger Yorkie but I know of a 4lb and 5lb yorkie who are treated the same way. If you keep her inside all the time, she will learn that the outdoors is a big scary place and it really shouldn't be.
They may be small, but they are terriers, first and foremost! Give 'em some warm clothing and they should be ready to go.
Check out alaskayorkie's Jillie -- prime example of an awesome little dog who roughs and toughs Alaska, and was taught to enjoy it or at least tolerate it.
Just thought I'd throw my opinion out there even if it's unwanted, lol