If you don't talk about this, she will continue this behavior and it might be difficult to change it later.

Since you're saying that you're closer to that couple, you should talk about it with either your friend or his wife. Though, it is better to talk with his wife if you and her are also close and she also respects you.

If you are about to talk about it with his wife, say something like,

>I have been noticing that you go via caretaker's room to get to garden quickly. However, it is not a good idea to do this without caretaker's consent, since she might be doing some work and not want to be disturbed. You should care about her privacy. While it is okay to do it sometimes after asking her, but let's not make it a habit.

>Just imagine if you were in that room not wanting to be disturbed and I pass through it, how would you feel? She's been working here for more than 20 years. It's her workplace and home as well. Can't we do at least this small thing for her? Please go via other way. It will take only 10 seconds more and won't harm you.

If you are going to talk about it with your friend, try something similar to above.

**Non-IPS solution:**

You can ask caretaker to keep her room locked from inside if it can work. You can also convince your friend to change caretaker's room if possible. Though this is not an IPS solution, but it will work.