Use of 1 PC and multiple accounts for Sims 4

Hello,

I had a question re. the use of Origin for Sims 4. I was hoping you may be able to help. I've looked at similar threads but the answer isn't completely clear. Scenario as follows:

• I have an Origin account. I have Sims 4 installed on my gaming laptop.
• My girlfriend has an Origin account with her own copy of Sims 4 installed on her laptop.
• My girlfriend wants to setup her Origin account on a separate user account on my laptop so that when I'm not using it, she can use mine [it is a higher performance machine and better to use than her own]. 
• Although we both own the game on separate accounts, she has a few more expansion packs than I do and so our copies aren't identical.

In an ideal world, I see this as working as follows: I have the game installed via my user account and play via my Origin account. She goes to play on her Windows user account via my PC, with her own Origin account, and is able to play the Sims 4 through the installation from my account [presumably a shared folder rather than downloading twice]. Any additional packs she has will install, though will not be accessible when I play via my own account.

Is my above 'ideal world' understanding correct, in which case we can use it as we'd like to - or will this not work for our purpose and we'll have to install the game twice on the same machine across two separate user accounts?

Many thanks for your help.

Josh