Speaking of parents not wanting to distress their children - my mother... I've been seeing scary parallels between my wife and mother (sense of entitlement, inability to handle stress to name a few). My mother has put awful burdens on a couple of my siblings...
So yeah... I worry about this kind of thing happening with my wife. I'm trying to take care of my end of things long term but have no idea what my wife is going to do if our marriage doesn't work out. I really don't think she can control her spending. All she seems to care about is today. She's not able to delay gratification.
It is good you are in therapy. Our family of origin does influence who we are with as a partner. I have had to work on my own freeze and fawn, co-dependent tendencies.
Attempting to change BPD mother's spending was impossible. I tried, her family members tried. It did feel like dealing with an addict who couldn't manage being cut of from her supply. But she also didn't seem to have a real concept of money- because her needs, and many wants, had been provided for, regardless of what she spent. When my father was working, if she spent money, there was more.
Eventually though- after retirement, the inflow of money changes and people need to learn how to manage that. The reality is that- if your wife continues her spending after retirement, the result could be dire. BPD mother had a monthly sum of money and in addition, she spent all her savings, and then, the house- without us knowing it. I don't know if she ever intended to tell us. But speaking to her, she seemed to not understand the consequences of what she did.
Her funds were so low, that she was in danger of the house being repossessed by the bank. And she was elderly, and needed assisted living help. What I had assumed was that- by the time she needed this, we could sell the house and use that money to pay for help for her. But now, unknown to us, she'd leveraged the house too.
Seeing my concern over this, she cornered me, insinuating I was after the house as an inheritance. My reply to her was "I don't care if the bank takes the house then, I care if the bank takes the house now, while you are in it". She acted shocked, she had no idea the bank could do that.
The only thing that stopped her spending was low funds in her account. I even consulted an attorney to see if I could intervene, but as long as she was legally competent, we could not. We'd not have let her go without essentials, but we had to have a boundary, and BPD mother would challenge boundaries.
She'd call me with requests for things she didn't need. Items it would be draconian to refuse her. She'd call and say she was cold and needed a blanket or a sweater. But she had several blankets and sweaters. Truly, I'd have loved to give her a blanket, or a sweater, if I thought she'd actually like it, but I had seen this dynamic enough to know that this wasn't about a blanket. She didn't want a blanket. This was a manipulation.
With money though- there is a boundary. If all the money is spent, there's none left. If you leverage the house, the bank can take it. While your concern for your wife is how she could manage, at some point, there is a limit. Consider is it better for her to learn it now, while the two of you are working and independent?