FLTC, First, does W work? Also, do you know what your monthly bills actually are to maintain the household? Are you still paying the 9K for D? Will this end anytime soon if you are still paying it?
As for what your W has squirreled away. I don't know the exact "legal" terms but your A can hire an auditor to see where she has/had money. Any activity in her accts will be audited 5 yrs in the past. This will be expensive but it's something you may have to do. All the more reason for you to be squirreling away money now. NH, is right, you need to see an A ASAP.
Also, I don't think it would be unreasonable for you to tell D that, under the circumstances, you can't afford to send her to Vietnam, right now. After all, you've been paying the 9K per month to keep her safe and away from W, right?