Lara who was running around getting into position to attack felt a little bit excited. Now that she was alone she didn't need to worry about defense and can go all out. When she was attacking with the others a portion of her attention was directed into protecting the warriors fighting beside her. So now that she was given the chance to finally let loose she was truly utterly excited.
When she was inside the dungeon she couldn't go all out since they were underground and she was scared of causing too much damage and breaking the dungeon making them unable to leave. Also, the enemies at that time were really strong, making her feel unsure of how strong she really was. So now that she was in a bigger field above ground, with numerous enemies that were basically small fry, Lara couldn't help herself as she felt super excited.
