Steph is there because Babs sent her. One of the inhabitants has a friend who'd made it to the safe house, and had frantically been calling to ask for help. Help is a nineteen year old human in purple body armour, but beggers can't be choosers.

She's picked a spot in a nearby house to do an extremely quick bit of recon, when she sees Lyla walk past through one of the windows. In a flash, she's run to the front door and pulled it open.

"Wait," she's trying to be quiet, not wanting to draw the attention of those creatures before she's ready to fight them. She tries not to make a judgement of Lyla yet - not all people are what they seem - but Steph's almost instinctive worry has kicked in anyway.