My Ex-wife Has Started Missing Payments On A Joint Loan, Any Options?

I 34M Location: Pennsylvania cosigned a student loan refinance with a current balance of around 9k (~500 monthly payment) with my ex wife back when we were together. Our divorce was highly amicable, to the point that our lawyers remarked that it never goes this well, and as part of it we each agreed to take our own debt with us as we left. It is spelled out in the divorce agreement what we are each responsible for, and says that if one of us needs to make a payment on the loan that the other should pay it back. My ex has begun missing payments on this last piece of debt between us, likely due to a change in profession resulting in her having inconsistent income. So far she has made the payments in time to not have anything hit my credit, but it's been close and is a recurring issue. Complicating this is that after 3 years of us being amicable she has decided that we should go no contact. I'm OK with this except for the part where she owes money in my name.

I've offered to cover the difference in total lifetime cost of the loan if she refinances, but she has not responded to this offer and I suspect she re-blocked me anyway. My concern is that she will simply stop paying and I'll be forced to pick up the payments to protect my credit. I can afford this, but obviously don't want to. While it is specified in our divorce agreement that she would have to pay me back, there's no enforcement mechanism called out, and if she simply doesn't respond to my emails/calls I'd have to...serve her papers or something? So asking: What are my options in the case things go south, and do you folks have any ideas for resolving this matter more efficiently?