Sounds as if your problem is with your ex, not with the refinancing process. You say she refuses "to provide the pay off amount on the mortgage." Well, if she's refusing to do that--the first step--sounds as if she's certainly not going to cooperate in the further steps necessary. So--and I'm not a lawyer, so this isn't legal advice--sounds as if she's in violation of the divorce decree. If she's refusing to provide the payoff amount and she's the only one on the mortgage, there may not be much you can do short of getting the court to order her to provide the amount.
On the other hand, it's understandable that she isn't going to voluntarily remove her name from the title. If she did so, you'd own the property and she'd still be on the mortgage. Yes, I understand that your intent (per the stipulation) is to refinance in your name, so that both the title and the mortgage are in your name. But it's not in her interest to remove herself from the title while she's still on the mortgage.
What makes you think that if you came up with $150,000, that she'd allow the mortgage to be paid off? In fact, since you can't get the payoff amount, what makes you think that the figure is $150,000?
If she's willing to sell, I could see an investor buying it from her, then reselling to you. That's an expensive way to do it, both due to the two closings and because the investor is going to want to make a profit from the transaction. But that's certainly doable. There's money out there--called transactional funding--that allows an investor to borrow money for a purchase and then (either the same day or within a couple of days) sell it to someone else. The money itself will cost the investor several percentage points--let's say $3,000. Then the investor will want to make a profit--let's say $7,000. So that's $10,000 plus whatever fees are charged in California for each closing.
The catch there is that she's going to have to agree to sell to the investor. And I keep coming back to her failing to provide the payoff amount. Is she doing that just to cause trouble? Or does she not understand the process? If it's not understanding the process, then the investor might have a chance. If she's just trying to cause trouble, then you may have to have the court compel her to act.
And one totally unrelated issue: Reverse mortgages are seldom a good idea. They have huge up-front costs and all sorts of catches. If you've investigated the subject and really feel comfortable with it, fine. But if you're just trusting someone who's told you it's a good idea, you really need to investigate that further. Check with your accountant or tax planner for more details.
Hope that helps.