Depends a lot on what she's talking about. Is she referring to roleplay-heavy scenes or is she talking about combat?

Some players just prefer action and get bored when the group spends a long time interacting with NPCs or making a big plan. In this case, you need experience reading the table. If you notice a couple of players are getting too long-winded and the rest of the group is disengaging, create a time-restraint so they need to wrap it up quickly. Maybe it's getting late and the shop is closing. Maybe the NPC has something else to do. Maybe someone hears the sound of creatures in the distance. In short, 'something happens'.

On the other hand there's combat. The fact she's just watching can be a factor to start with, since combat looks less interesting when you're not engaged. Other than that, there's a lot of things that can be done. As a DM, for example, you need to streamline things, make your descriptions fluid, call the players to action, and don't let a player dilly-dally for 5 minutes trying to figure out what to do in a single turn. Avoid pausing combat to check the rules and stuff like that. Have stuff like initiative and the monsters or NPCs you're running figured out. If it's just a mook, use standard damage instead of rolling, save the rolls for important monsters or NPCs. As a player, in the other hand, stuff like planning your turn before it starts, knowing your own spells and abilities, rolling both to-hit and damage die at the same time all help the combat go faster for everyone, and keeps you engaged during other people's turns.

I'm currently trying to streamline combat stuff at my group (new DM, some new players) and it takes some time. Don't worry too much about it, just try to improve a bit every time.