We have discussed this in the past, but not recently.  

 
Assuming she didn't do something egregious to you, and you'd like to not only avoid drama but preserve the potential for "just for old times" one-off BCDs down the line, here's my suggested approach:  

 
1. Just like negotiating starting allowance, it's about you (specifically YOUR budget), not her. Tell her that something beyond your control changed in your life; lost/changed jobs, significant increase in expenses due (sick relative, lawsuit, stock losses, debt/loans coming due, etc.).  
2. As a result, it's no longer practical/possible to provide her allowance on an ongoing basis based on your new budget.
3. You will understand if she needs to move on, as you respect her life's struggles and support any decision she needs to make to ensure her success.  
4. Wrap it up with sincere admiration for her "as a person" (try not to barf when you say that part), and would love to stay good friends and be her mentor IF she decides to move on.

 
Why do all this?  
1. Eliminates the blame game.  It's not her "fault," it's yours.  
2. Blocks any arguments about her "worth."  She is and will continue to be amazing!  
3. If the reason is beyond your control, it's definitely beyond her control.  
4. Gives the appearance that the break-up decision is entirely hers. She controls her destiny.
5. Leaves the door open for "something" down the line.  
6. Since she makes the decision, as long as she believes you are sincere, she has no reason to trash you.  

 
I have had a few occasions to use this strategy.  In most cases, the separation was neutral (i.e.: a win).  In one, she made a significant effort to try to come back to me 6 months down the road, which resulted in 3 no-allowance BCD's before SHE realized it wasn't going to happen (note that again, I let her think the decision was hers!).  Interestingly, I just heard from her last month: she has a new job/career and is moving to a new apartment using her own now-improved credit score. She thanked me for helping her learn financial management skills, professional discipline (show up on time, deliver on promises, etc.), and how to plan and focus on objectives.  Add in all the great BB sex, spontaneous BBBJ's (including a significant amount of road head), and her hooking me up (although unknowingly) with her hot stripper friend, and I consider this as one of my best arrangements ever.  

 
Please let us know what you do and how it went.  Thanks for sharing the question.  

 
Life is good

 
The Cat