Most of the lines are actually wheelchair and ECV accessible, so in many cases, she will be waiting in the regular lines. Except for the time around Thanksgiving, WDW is typically not that busy in November, so the lines should actually be short.
I know you've read the FAQs, so I'll direct you to some parts of it that might be particularly helpful. In post 3 of that thread, there are some links to the official WDW website information about guests with disabilities. The one labeled "Mobility Page" includes a list of the attractions where the entire attraction is wheelchair and ECV accessible (so she could ride the ECV in line and stay in it for the whole attraction). There is also a list there of the attractions where the line is accessible, but she will need to transfer. You can get a copy of the Guidebooks for Guests with Disabilities at each park, but the stuff on the Mobility Page is more concise on the webpage, so I'd suggest copying that and printing it.
Also on post 3 of the disABILITIES FAQs thread, the first link in the "Un-official Links" is about boarding rides for someone who needs more time. The person who asked the question originally was not using an ECV or wheelchair, so there was some advice for her to request a GAC. Your friend won't need a GAC, but some of the other information on that thread - like which rides have moving walkways - would be helpful. If you can't pick out the pertinent parts, PM me and I'll cut and paste and send it to you as a doc file or a pdf file so she can have just the parts she needs.
Deb Wills' site has an attraction ride car section that shows what the ride cars look like. Her pictures were mostly for Pooh size people to judge how comfortable the seats are, but may be helpful for your friend to decide whether or not she can board them and/or how she could. There is also a new
website with information for people traveling with wheelchairs that has some good descriptions.
For the stoller, I agree that the 6 year old may do very well with walking and they could easily rent a stroller at the park for her if she turns out to need one. My older DD had to walk when we went to WDW when she was 6 because the strollers then were more for 2-4 yr olds. She complained some, but really kept up quite well.
As for the one year old, they should bring a stroller for her. The WDW strollers are good for older toddlers, but not really for a baby. Here's a
link to Deb Wills' site with pictures of the WDW strollers.
We rented an ECV a little over a year ago from Randy's. They were excellent and delivered it right to the room rather than to Bell Services. We had a phone number to call once we had our room so that we could arrange for the delivery. The guy who delivered it demonstrated it and would have shown us how to take it apart and put it together if we had planned to transport it by car or van.
For the van, most of the ones we have rented only had 7 seats; I think there may be vans and some
ECVs that seat 8. You might have to look a little for that though.
I third the suggestion to look into a power wheelchair now. My DD just got a new power wheelchair in March. We had actually started the process last July. And, it was not her first power wheelchair. So, it's better to get the process started and get it faster than expected than to be waiting for it when she really needs it. For her back, the ECVs have a seat similar to an office chair and some don't have very good back support. I know some people have gotten a back support similar to
this one from Office Max. Several people I know who have back problems carry one like that around and put it on any chair they sit on. It doesn't necessarily need to be strapped in like on the picture.
Good luck and sending lots of pixie dust for their trip