Surprised by Mother-in-law

My wife was away for the day and I was in the back yard vacuuming the swimming pool in the nude. The house was locked so there was little chance that I would be “surprised”. My mother-in –law had a key to the house and let herself in, walked through the house and came out the back calling out a greeting. There she was, standing by the table where I had left my very brief bikini underwear, and I had to walk around the pool in full view and up to her to find any cover at all. Now this is an older woman with a strict religious upbringing who I assumed would be shocked by what she saw. I welcomed her, asked if she would like a cup of coffee, and she accepted and went inside. I stopped to put on my red briefs, just a couple of tiny red triangles really, and proceeded to the kitchen to make coffee. I decided given what she had already seen, there was no point in putting on more. We had a nice visit and she left for home. I expected she would express her disapproval to my wife (she seemed to disapprove of almost everything we did, and was never reluctant to point out our shortcomings) but to my amazement it was never mentioned. Thinking back, if I could do it over again, I would remain nude and only put on something if she asked.