The assumption here is that your manager is physically invited to the
projects she's managing teams for, and might also be a physically invited to
other projects she's simply participating in. So how do we focus on the
ones she's managing?
The Projects Tab only shows those projects that the user is a physical
member of, so the Projects Tab is already filtering non relevant projects in
that respect. The next step is to establish which of those projects your
user is actually managing teams over that she needs to see and get rid of the peripheral
projects she's simply participating in.
You will need to utilize the "Manager" native field and set it to
that user's name, or come up with your own custom field and designate your
user. This will allow that user to then Filter on the Projects Tab only
those where her name is set in the Views setup. This will allow her
to distinguish projects she’s managing vs. projects she's participating in.
She could also filter on Project Role, but this assumes her role in the projects she's managing is as Project Manager - this would free up the fields.