It's quite possible for malware (not necessarily viruses) to affect one account and not another as different programs and settings will load with different users. The first thing to do is download a free program called CCleaner (you can get it from numerous places, but I would suggest Filehippo). This has a number of useful functions, firstly, on your wife's account run the 'Cleaner' section to get rid of unwanted temporary files etc. - these build up doing web browsing and can slow down your machine, then click on the 'Tools' section and select 'startup'. Go down the list of programs that start when the system starts and compare them to the ones that start when you log into your account - you will find she has a lot more things starting, and the majority of them can be deleted or disabled using CCleaner. Once you've done that, see if things have improved.
If not then you may have some malware actually running in the background, so download and run Malwarebytes (again, available from Filehippo). It is a shareware program but the basic scanner is free to use - make sure you remove the tick from the 'trial version' option during installation. Do a quick scan and remove anything that it finds (don't do a full scan immediately as I have had instances where this can cause damage if the wrong files are removed).