OK, well here's something else to try...
Based on your problems sounding rather similar to those in the threads I linked to earlier, and several others going back to El Capitan; most of which were seemingly due to a launchservices process crashing for one user, and resolved by removing several or even all files within /private/var/folders.
Since it's just one account, the whole folder approach seems unwise, so let's try to remove just the one in question; without too much Terminal.
I've tested this here on Sierra 10.12.6, the removed file is replaced as soon as the user logs in again. There may be no improvement for you, but it's fairly quick & easy.
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Logout of the problem account if it's active.
Open this webpage in the good account.
in Terminal, from a working Admin account enter the following command :
su problem_account_name
substituting the actual problem account name for problem_account_name
If your problem account is named Dylan : you'll type su Dylan then press enter/return
You should get a prompt for a password : enter the password for the problem account (it won't be shown on screen) then press enter/return. A new Terminal prompt should appear.
type the command id followed by enter/return : the output should confirm that you are working as the problem user (name should be in brackets, as below; the numbers aren't vital).
uid=502(Dylan) gid=20(staff) groups=20(staff)...
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Copy the following text, and paste it into Terminal, followed by enter/return:
open `getconf DARWIN_USER_TEMP_DIR`../0
A Finder window should open, showing a folder named 0, and inlcuding a file name similar to
com.apple.LaunchServices-175-v2.csstore as well as some folders showing the 'no access' icon.
See the screenshot below :
Select the com.apple.LaunchServices... file & trash it, providing an admin name/password when prompted by Finder.
go back to Terminal, type the command exit followed by enter/return
Restart the computer, and try to login to the problem account.
