Advice on How to Handle Issue with Nanny

We had a nanny start with us last Thursday in preparation for my going back to work on Monday. Since Monday, our nanny has been late two times. The first was on Tuesday and she was late by 25 minutes. This was because the one of the people from the nanny service was dropping her off. The second time was this morning and she was late by 20 minutes because the bus was running late. I want to have a good relationship with her but need her to understand that when she's late, I get to work later than I want to (especially since I'm trying to get home earlier to spend time with the kids before they go to bed). I understand that this being the first week we are both getting used to commutes and want to be sensitive with that. I would appreciate any advice that you all have on how to handle.