I'm being mindful of not allowing her to make a bad investment.
May I suggest you change your verbiage or discussions with her to elaborate on "investment". 99% of cars are just depreciating assets, the other 1% are collector cars which isn't what's she's looking at. As she considers each vehicle, consider the total cost of ownership. An Audi will have higher insurance and maintenance costs compared to a Chevy to the tune of maybe $1000 per year.
Based on the Cruze or used Audi, I'm guessing she's in the the mid $20K range for price. I'd like to suggest she really stretches out her search criteria, including looking at some older vehicles. Cars made in this century are so much better built and last a lot longer than those of yesteryear. Don't be afraid of looking at cars that may be 8 years old.
Mrs. Zoom and I have 6 cars. With the exception of the new truck (I allow myself a new truck every 10-12 years), all of ours are older but still damn near bulletproof if you buy the right model for the year. There's a lot of web sites that give detailed information by year for the style of vehicle you're looking for. As an example based on our most recent purchase, I ended up on US News and World Report's site of rating mid-sized luxury SUV's. The ratings pointed me in the right direction as the top 10
were all the Lexus RX-350, just different years or trim types.
Once we've narrowed down the top couple vehicles, one of our strategies is to look for vehicles owned by senior citizens for multiple reasons. They're almost always dealer maintained at precise maintenance intervals; most are low miles since they're not driving to work daily; clean since they don't haul rug-rats or daily living crap; owners are established at household so they're normally garage kept; most are one-owner cars... A CarFax helps recognize who the previous owner(s) were.
Our go-to sedans are both 15 years old. Both were one-owner senior citizen cars, dealer maintained, low miles... like what I discussed above. Great deals are there to be had. Our Lexus SUV is 8 years old but only has 54K miles and again, a senior's car. It's 100% immaculate inside and out.