How long am I ''supposed'' to meditate for anyways?

That is pretty dismissive, to suggest that she needs to be 100 percent present 100 percent of the time.
Meditation helps teach presence. Self taught, yes.

Some people are new to the very concept.

The simplest answer to how long, or how to increase time is sit. Just sit.
If you need to focus on something, do it. If you are helped by a mantra, do it ( but not if you are the only chanter in a roomful. Please)
If picturing puppies prancing in a puddle gets your mind in a theta wave area, do it.

No one person has the ultimate answer to meditation because it has many sources and many flows.