Thank you for your question.
What you want to do is ask her why she has been coming home late from work. Tell her that you noticed changes in her normal routine.
I want you to think positive and not think about her cheating because their could be a good reason why she has been late.
One thing that should ease your mind is that there is no evidence of cheating you mentioned, so I feel it is something else.
One thing you do not want to do is accuse her of cheating or make her feel uncomfortable.
If you approach it the wrong way she will automatically look guilty even when she is not. So you want to say this, "I couldn't help but notice you have been coming in at a different time. Have you been working later or has their been extra traffic?
She will answer you on what she has been doing. If she does not answer the question then she has no answer.
The reason why she would have no answer is because she would have to come up with one. If she is not doing anything she will just give you a straight answer to all your questions. If you ask her in a negative way she might just respond back in a negative way, so you want to confront the issue with just a simple few questions.
Even just mention it when you are both relaxed and everything is settled so she can answer you correctly.
You want to confront the issue because you do not want to keep thinking that she is cheating.
You want to clear your mind of those thoughts and not wonder why she is coming home late from work.
There could be many reasons why she is coming home late. I am sure there is a good reason and I feel that you should ask to ease your mind.