Is it definite that the chinchilla simply won't jump, not that she can't jump? My concern would be that she might have and underlying medical reason for refusing to jump and doing that odd 'walking' everywhere. Perhaps she has arthritis, a back injury, or some other impairment? The main reason I am wondering this is that it is something so basic as an animal's standard mode of locomotion is pretty ingrained in them biologically and should come naturally even if they are denied the ability to do it for a prolonged period of time in the overwhelming majority of animals.
Also, getting back to you about mice finally!
I personally think a 10g isn't appropriate for three females. It's SAID to be OK, but given how active the species is, I can't imagine three girls having enough space in that size tank. If you plan to do this, I'd go with a larger tank, at least a 15g or preferably a 20g long. The other option if you definitely can't do that would perhaps be to add an under-bedding tunnel system AND a second floor, but that can be tricky in an aquarium (and under-bedding tunnel systems are a PITA to clean).
A cage topper can be an option, but there's only one cage topper I'd EVER suggest as appropriate for rodents: the Zilla Fresh Air Terrarium Top. It has TINY bar spacing, basically it's a fine grid. I've used it for itty bitty little anoles and the like with no issue, as well as with rodents (currently using with my ASFs). You do have to build additional floors, however, as it does not come with them since it is more for arboreal lizards.
Toymaking... really you can use anything you use with chins, rats, bunnies. My mice like everything from those cheep plastic budgie toys that are basically a chain of plastic balls with bells inside, to big complicated wooden and fleece creations. They like sissal ropes to climb around on, hammocks, chew toys, manipulation toys, foraging boxes, paper towel rolls, cholla wood, novel scent toys, the whole nine yards. They don't seem to chew plastic as badly as chins/rats, so I even use some plastic toy parts. You can really go wild making rodent toys. I'd check out the DIY toy thread on thefunmouse forum if you haven't already.
