I think "showing" vs "lecturing" is the right path to go down. If someone doesn't want to move over to the MMM or even just a "more frugal" lifestyle then pressing them to do so is just going to cause more problems. I have more or less been maxing out my 401k and Roth IRA since I was 23. In this community that may be normal, but in the real world it's very rare. I could get behind doing it myself b/c I had a conversation with my father who suggested it while I was living at home for 2 years after collect. My parents are frugal (when they had young kids) and are more relaxed with money now in their retirement, but they didn't practice what them preached in terms of investing, so it's funny that my father made the suggestion to me. So while I was living at home I maxed out my accounts and saw how doable it was, and when I had my own place that just became a part of the norm so that's what I went with. My wife and I got married about 4 years later and I was already on that train. She didn't have high paying jobs though so really couldn't do it, but I convinced her with her first job to at least put away what she would get matching for because otherwise it was just throwing away money (literally). She saw how not saving to get a match was silly, so she started from there and each raise put in half of that raise towards her 401k. When she got higher paying jobs she put more and more in, and for the last few years she's been maxing out her 401k as well! She wasn't always a super saver, in fact she was very bad with finances, but I led by example and was not shy about telling/showing her how I was saving and how important it is.
I do the same thing with my sisters and they have slowly come around. If you show someone a simple compound interest calculator and show how much ditching that starbucks every day and brewing at home will save you over a lifetime, it's pretty amazing. A $5 starbucks each day is $150/month, invested each month at 8% in the market and over 30 years that's $0.25M. I'm not taking about $1k or something, but a quarter of a million dollars. If brewing folgers coffee at home becomes the new normal and you can save and invest the rest and you can really SHOW how the savings and frugality leads to real results then they can slowly move over.
For the joint accounts, and what you suggest, that's exactly what the Mrs. and I do, but we didn't start until after we were married. We bought our first condo together right when we got married and that's when we got a joint account, but each kept separate individual accounts as well for personal expenses. That includes normal grocery visits, gas, food, whatever, but our joint account was for mortgage, utilities, 529 plan investments, whatever is joint. We also didn't both split 50/50. You may be making more and saving more but your significant other may need more take home money b/c clothes cost more or they have a gas guzzler or they buy groceries more, whatever. Try not to use this against her, show her how much more you're saving and where it is going and what it'll be worth in 10/20/30/40 years if they continue on that path. SHOW HER what it'll take for her to be a millionaire on her own terms. I tell my wife that she'll be a millionaire all by herself some day and I think she gets excited about that! It's taken time but if you can show her and not just tell her about saving money, get excited about how you cut the cable or reduced your cell phone, or how you bike to work or save in normal everyday things then that will slowly start to sink it. It's a process though, it won't happen overnight and you can't put that pressure on to do it overnight or it will sour the relationship. Have her read a few articles, get her excited about saving, have her think of purchases (that are unnecessary) as extended work and it'll start to sink in. My sister bought a $65k car and I told her that that just means she'll be working an extra few years so they can "enjoy" the commute to work. It'll start sinking in though, some faster than others. I'm lucky that my wife had it sink it a lot faster, some it will not sink in at all, so you'll have to lead by example for a while but I'm sure those roots will start taking at some point, hopefully sooner than later! Good luck!