My suggestion would be try not to make it about money. Strange suggestion, I know, but hear me out.
Before MMM I had resigned myself to working to 70 and never owning a home/property. I didn't think it was possible. Now that I know it can be, if I work at it, I feel motivated to cut out mindless spending.
You've mentioned that she enjoys her job, which is wonderful for her, but she might not always enjoy it. Toxic coworkers and bosses do happen. What would she do if she started to dislike, or even hate, her job? Could she up and quit?
More so than fear mongering, though, I would try to figure out what's important to her. My priority is stability and security. To know that I don't have to move for the 22nd time in my life (no exaggeration) once I get into a home that I own (really, I'd be slowly buying it from the bank, but anyway) would be so much better than new bras every 2 months.
On the topic of bras, too, you might subtly mention that you noticed some research that proved they're only
cosmetic fashion accessories. Sales people tell customers that bras wear out every 6 months but I haven't found this to be the case unless the band (the bit that goes around the ribs) is mostly lace. She may think that she needs to replace them often to reap some (false) benefit. That said, I wear them for fashion reasons these days as I'm otherwise self conscious.
Also, people don't notice if you wear the same outfit often. You could introduce her to the idea of a
'work uniform' - posing it as saving her time and
decision fatigue rather than making it about money. This might have a higher initial cost, when she picks out the uniform and gets 5 of everything, but it should save time and money down the road as she'll have less incentive to impulse buy clothing for work - if she likes the idea which, admittedly, she may not but it's worth a shot.
I also second the suggestion that you could pick up the grocery shopping, meal planning and cooking. You can get the best price and hone a skill as well as likely win points for taking up these chores.
What has helped my stress level and my spouse's understand is making it a conversation about our lives together - about what we value, our financial goals and how we want to spend our time (not me at the office for another 40 years). I hope this is helpful and I wish you the best of luck convincing her.
Edited: Typos