Please, please, please tell your friend that using an ECV is not a "cop out". It's not a "fail". It's simply using the best possible available TOOL to get the most possible enjoyment from your shared vacation.
If she needs glasses, does she refuse to wear them, going through life squinting at everyone and everything? Probably not.
If she needs to use a calculator to do math, does she refuse to touch it, and instead resort to pencil and paper - or counting on her toes and fingers? Probably not.
Both of those - glasses and calculators - are TOOLS that we use every day to make our lives more efficient. At WDW, many people use an ECV as a tool to improve both their stamina, and their enjoyment of the vacation. It can help with pain management as well. If she wants to walk from time to time, you can take a turn behind the wheel so that she can stretch her legs and move a bit.
You will not find a tour that balances walking and sitting. Similarly, you will not find many benches at all in any of the theme parks now - or the Disney Springs area. We were just there last week - on more than one occasion our daughter simply gave up and sat on the ground when there was no seating available and she needed to take a break.
Typically the WDW
ECVs rent out fairly early in the day, and since you can "hop" the rental for the day from one park to the next, they are often in short supply. At $50/day (+ a $20/day deposit) it is typically cheaper to rent from a local vendor for any trip longer than 2 days.
Additionally, many people fail to factor in to their plans that it can be (at some WDW Resorts) quite a hike to the bus stops and to food services. Not to mention pools, laundry rooms, etc. And, if you intend to do Disney Springs (formerly known as Downtown Disney) it is significantly larger in size now - probably easily double the size from the last time your friend visited. With so much to see and do there alone, we now plan a dedicated "downtown day" for every trip.
There are many people who rent ECVs only at WDW - in their "regular" lives, they never need one or use one. If your friend is worried about other peoples perceptions of her, tell her not to. The likelihood that she will EVER see any other guest from WDW again is so incredibly tiny that she has a better chance of getting hit by lightning AND winning the lottery in the same day.
I hope you enjoy Flower & Garden; it is one of my favorite times of the year at WDW!