Lena knew that since it was Jeff who was not familiar with the route to and from this estate to Samuel's house that it would take him longer than it would've taken Clive to go and pick up the other, but the time difference was making her impatient.
Samuel had texted her to let her know that he was about an hour out according to Jeff - meaning that he would again be in time for dinner. However, it had been over an hour since he had sent her that message and she had yet to see or hear any sign that they had arrived.
It wasn't that she was worried that anything had happened to the little chickadee himself, more that she was worried Jeff would end up getting lost despite using the navigation device and would end up arriving far later than they had been scheduled to be.