Indecision can be so frustrating. If you push too hard or too fast they will blow up. If you don't push enough they will let the subject disappear and never be answered. The key is to find just the right amount of pressure.
We have a communiation tool called
D.E.A.R.M.A.N. that I think will work very well here. As always when trying to get your pwBPD to hear something they don't want to hear, it requires a lot of finessing with validation before hand.
So for instance in your scenario, having the conversation might look something like this:
"I know you're really busy and that scheduling one more thing can be overwhelming (
addresses her excuses). I'm worried about D too. It's scary not understanding what is going on with her (
validates your wife's worries). It's important that we meet with D's teachers so that she can start getting the help she needs at school (
states a truth). Can we take a look at your schedule together (
offering support and comfort) and choose a time that works best for you to meet with the school? (
puts the responsibility back on her)"
If at that point, she continues to stall, it might require using a little more pushback or putting a deadline on things. If she still balks, you might try:
"I know this is a difficult time, but the longer we put this off, the longer the problems at school will continue. Can you schedule a time with the teachers before next week, please? I know it's important to you that you are able to be there. It's important to me too. But if your schedule won't allow it, I'm going to set up the meeting for next Friday (or whenever). I would love for us to go together, but if you can't make it, I understand. I'll update you on what is said after we meet."
Taking this idea and looking at DEARMAN, can you try to create your own dialogue here before sharing it with your W?