You are overthinking this and, I think, getting lost in the weeds. You are doing the right thing rolling everything over to Vanguard. How much of her funds do you think she might need within the next 5-10 years? Put that amount in a CD or bonds. Put the rest in VTSAX. Re-evaluate and revise as your and her circumstances change. That way you have the "possible short-term money" completely safe, and are getting better returns for the long-term money.
You really don't need to worry about having multiple complex asset allocations in each of her separate accounts -- what matters is her overall allocation across all of the accounts together. You should be able to combine all of the traditional IRAs and 401(k)s into a single account at Vanguard (the government views everything as one IRA anyway), so start thinking big-picture instead of getting lost in the complexities of individual accounts.
SS: if she was married for at least 10 years, she would be entitled to her ex's SS. But in any event, as long as you can support her, she should postpone claiming SS until 70, because at that minimal amount, the increase she'd get from waiting would be critical for the long-run in case at some point you are not able to support her any more.
Taxes: you have time to research this. Generally, taking money from IRAs and such is considered taxable income, and selling taxable accounts triggers capital gains -- but there is a $12K standard deduction that makes any income below that free from federal tax, and the CG rate is 0% for people in that tax bracket. BUT I do not know how these rules apply if she is your dependent for tax purposes, so that is something to look into as she gets to the point of needing to withdraw money.
Stay away from Betterment. There is no fundamental difference between the kinds of funds you are looking at, and anyone who tells you different is bullshitting you and you should run in the opposite direction on general principles. So go with the lowest-fee option.
Finally, you are really underestimating the impact of a 2% difference in returns in the same way most people do, as a one-time thing vs. a difference that compounds dramatically over time (which is exactly why some funds can stay in business while still charging 1-2% in fees!). The rule of 72 says that the rate of return of an investment times the time until the investment doubles equals 72. So if you get a 10% return, your money will double in about 7 years, whereas if you get an 8% return, it will take 9 years to double. And that happens every 7 or 9 years. So assume you decide to invest $50K of her money, and she lives another 35 years or so. If you get a 10% return, that will double every 7-ish years, so she will get 5 doublings in 35 years -- so in 7 years, she will have $100K, in 14, $200K, in 21, $400K, in 28, $800K, and in 35, $1.6M. All from $50K! OTOH, if you get an 8% return, it will take 9 years to get to that first $100K, 18 years to $200K, 27 years to $400K, and at the end of the 35 years, she won't even have $800K. She will have less than half as much, all because of that "little" 2% difference.
Now obviously that is just an illustration, because she will be drawing on that money before then! But that difference in returns illustrates why it is so important that for however long you can continue to support her, she needs to keep her own funds aggressively invested, because she is going to need to maximize the returns off of her relatively small investments if she is going to be able to support herself if and when you no longer can.
