I'd leave your sister in peace. If she'd object to Firefox, she'd probably never forgive you for an OS change. Windows 7 will continue to be supported until 2015 and the odds of your sister needing a new computer by then are pretty high.
Internet Explorer is still in 10. It's under Windows something - I'd put an icon to it on her desktop and set the home page to Yahoo like she's used to.
I upgraded my windows 8.1 to 10 without much issue. I had to fix a few minor things but otherwise everything seems fine. Back to my original question, my Sister primarily uses her windows 7 computer to do email plus a little surfing, buying stuff and such with Internet Explorer. I use Firefox. Since she is so adverse to change, I haven't tried to install Firefox on her computer. I opened Microsoft Edge on my computer and here is where the issues begin.
1. Should I upgrade her computer, just because windows 7 will at some point be unsupported?
2. Right now her home page is Yahoo, where she can easily get to her email account. Is there a way to when she clicks on the Microsoft Edge 'icon', that it takes her directly to the “Yahoo.com” website? I saw that you can have 'another' tab, and set it for whatever 'site' you want. But the “Microsoft Edge” page opens as the 'home page'.
3. I have gotten her used to using the 'Favorites' in Internet Explorer, now I see that you have to “click” on that 'symbol' to get to 'Favorites' to the side of the screen, not a big thing I suppose, but still different.
4. Is Internet Explorer now “gone” if your using Microsoft Edge? I ask because, when I went to the “Dell” website, for my computer, it stated that I needed to use Internet Explorer. I'm assuming that Dell will get with the program regarding Microsoft Edge, but is this the thing to look forward too? If so, I'm sure that my sister will run into this sort of issue at some point.
5. There were a few 'apps' that I had to reinstall on my computer after the 'upgrade', so I'm inclined to believe that will also happen on my sisters HP computer as well. Creating more work for “me”. LOL
6. If the upgrade does not include all necessary drivers, I assume I will have to visit the HP website to get whatever is necessary, maybe also for her printer. Could take some time to set up.
I did make a DVD disc of Windows 10 to maybe make the process faster.
Anyway, thanks for any suggestions.