Photos aren't evidence of flooding and there is a lack of information there. And I doubt flood insurance would allow for new windows. In fact if she had sold it straight away, when ordered, this wouldn't now be an issue so she has created the issue in a way which may not look good. She has been responsible for the house and selling it before it deteriorated. If it did go to court she would have to prove it had been flooded and when and show any insurance claims. Maybe it has been flooded though.
When you say walls removed, do you mean plaster knocked off or actually walls knocked out?!
The not so good news is, if it actually has been flooded it could be very difficult to sell as buyers may have difficulty getting flood insurance. They would have to take over the existing policy I think (If the insurers allow that), or go with a specialist company maybe. Building societies won't lend on a house without flood insurance. But then there are a lot of people in that situation, so I think there are specialist insurance companies now.
If you want to check, you can do a couple of things. You can check with the postcode and address on here. It'll tell you if it's low, medium or high risk for flooding. Then underneath you can click on the map for visuals which shows the risks a bit clearer.
How to check the long term flood risk for an area in England, assess risk from rivers and sea, surface water, reservoirs, ground water.
www.gov.uk
But the main way to check if there has been recent flooding is just googling floods in that area and various things will come up (and youtube videos).
I guess he could reply asking if the house is subject to an insurance claim and if so could she forward the details please. You'd probably get another abusive response, but if she didn't send the details, then again she would look like she was lying if it went to court. If his name is on the deeds or he is still paying a mortgage on the place, he'd have every right to see details of any insurance claim.