Theme only showing up in old account/admin

Question:

1. Is it a multisite install?
2. Do you have full-admin access?

And if you don’t have multisite, you need to install the theme twice and both location of the wp-content/theme folder

Multisite is if you want to have network of WP sites with just one WP install. I guess you’re not using this one because you have two admin accounts.

You just have to upload the new theme on both WP install as follows

e.g. if on the same server
ftp://public_html/site1/wp-content/themes
ftp://public_html/site2/wp-content/themes