Carlin has an iMac that's about 6 years old and it's getting slower and slower. She brought it into a technician, who said it was too old to get parts for it. Leo says that's not really accurate. It's always best to take the iMac into the Apple Store when it needs repair or upgrading, and it can be upgraded.
But 5 years old isn't that old. Odds are, it's just full and she'll have to backup her data, format the hard drive and start over. Carlin should go to the store and get an external hard drive that can plug into her iMac. 1TB would be plenty. Then once she has it plugged in, she should boot it up and copy her data over to the external drive. There's a users folder, and she can just drag and drop it over to the external drive. She can also backup her images to the cloud, using Google Photos, Carbonite, etc.
Once the data is all copied over, she should shut it down. Then she should press CMD + R and turn it on while holding those two keys. When the apple appears, she can let go of the keys. Then select "erase" to erase the hard drive and reinstall macOS. That'll speed everything up. She doesn't really need a new computer, or spend money to upgrade it, unless she really wants to.
(Disclaimer: Carbonite is a sponsor)