Sorry, I'm not so tech savy, but a platter drive replaces the HD?
The hard drive that is in the laptop is called a "Platter" hard drive, because it is mechanical and uses multiple platters to store data on. They wear out over time. Especially on laptops. Also can be easily damaged, because they are so fragile for the size that is in laptops.
SSD drives have no moving parts, so less wear & tear. Also can withstand a drop.
As for the DVD you have. If Windows 8.1 64bit was installed and the version you have is 32bit. It can cause a problem when the disc is trying to look for a previously installed version.
As long as you can choose the DVD from F12, it should boot up to the DVD. You may have to go into the Bios settings and turn off Secure Boot. Press F2 or Fn + F2 to enter the Bios settings.
To change out the hard drive on the toshiba laptops, flip it over with the battery & power removed. There is a panel in the middle that should have two screws that have to be removed with a eyeglass phillips screwdriver. You take off the panel, then remove the one screw holding the tray for the install hard drive, pull it out, then remove the screws holding the drive to the tray and place the SSD in its place, reverse process.
Your wife will love you. Now if you can get her to use either Firefox or Chrome, and you install anti-malware preventative add-ons, like AdBlock Plus, McAfee Website Cert, Bit Defender Traffic Light, WOT (Web Of Trust), along with a good system anti-virus/anti-malware (Kaspersky is the best running so far for paid anti-virus software).
The last is getting her to change her habits by not opening untrusted attachments to emails she does not know the sender, along with staying away from certain malware laden websites, she should be fine.