I need some help regarding emptying my Mac book pro

Ok. However the best way to do this is to completely prepare it to be given to her. This will include removing your Apple ID "presence" from this notebook, then completely erasing it, and finally reinstalling macOS ... so she has a "clean" device to call her own. She can then use her Apple ID with it. After preparing it, you can help set it up for her and install any apps that you want her to have.

Take a look at the following support article on how to go about doing this. It may appear to be a bit elaborate, but it will save you any frustrations in the long run.

Ref: What to do before you sell, give away, or trade in your Mac - Apple Support

Is your goal to increase the storage space on your MacBook Pro? ... but, at the same time, retain its current operating system and apps?

This can basically be done in two different approaches:

1. Completely erase the Mac's system drive, and then, reinstall macOS. Then reinstall any required apps.
2. Attempt to remove as much data from the notebook without going through the same steps as in the first item.