I'm curious, what are you thinking will happen when she does retire? Do you think they are expecting some kind of support from you? In that case, I could see it being useful to have a conversation clarifying that that is not going to be an option (if that is the case).
If you are thinking they will just have to downsize their house+lifestyle, well then, I agree with the others that that is something they surely realize and will have to handle on their own.