We use MUS and love it, but if you’re already familiar with RS having used it with your other kids, I wonder why you’d want to pursue something different. I know that MUS goes in a different “order” from most public school math programs, so if it’s also different than RS (I don’t know if it does or not) it might be difficult to use both programs – other than as petitemom suggested with using MUS as the core and the RS games to supplement. I know MUS has some very particular to it terminology and ways of doing things, I’m not sure how that would mesh or conflict with RS, which also must have some particular ways of doing things if it requires transition lessons. If she’s already had a more traditional math program and is doing well with it, you might just want to stick to what seems the most familiar with her, as I’m sure there’s going to be so many other things she’s having to adjust to. Or it may be easier for you to stick with what you know, as I’m sure YOU are also having lots of other new things coming up without having to acquaint yourself with a new math program.
Different topic, but very excited to hear that you’ve adopted an older child from China – very exciting, I’m sure you’ll be super blessed by this dear child, and I know she’s blessed to have you as well!
Rebekah