There are two handles on the window, both of which had the same problem. This is it:
It was locked in that position. OK, so I can't move it back because of the lip; I can't move it forward because of the ridge. Why would I want to do either, though, when I can simply unlock it and move the handle out of the way? Ah, because I couldn't unlock it:
I could get the key in but I couldn't turn it.
I've no idea how my mother managed to put the window into that state, but I suspect it involved much brute strength. As for why she did it, I'm completely clueless; as, indeed, she is herself. All the while I was trying to fix it, she was telling me I couldn't do it and that she'd have to get the council to fix it and they'd probably need to take the window out and she hoped they wouldn't have to send someone from Southend and she'd tried for hours and there was nothing that could be done and I wouldn't be able to fix it.
I eventually did fix it. My younger daughter was able to push the window upwards (!) enough for me to be able to turn the key in the lock. At first, it seemed to make no difference and I suspected that the lock was broken (which is not an unusual thing as far as my mother is concerned — she's broken a key in a padlock before by forcing it to turn the wrong way instead of, you know, trying the other way just in case). Experimenting with another window, I realised that there was an alignment issue and that if I could get the handle to line up properly I should be able to press the button, so allowing me to turn the handle. A little persuasive force allowed me to test my theory and I got it so I could rotate the handle as its designer intended. I did the same at the other side and could finally close the window. I should probably have eaten the key at that point so she couldn't do it again.
My mother was intensely relieved at my success, so much so that she then proceeded to show my daughter all these new windows that had been installed since her last visit, which she hadn't wanted to mention earlier because to do so would have reminded her that she'd broken one of them.
I'd be worried that my mother was going senile if it weren't for the fact that she's had this uncomprehending attitide to technology her entire life. I'm seriously beginning to wonder if those stories she tells of my repeatedly locking her out of the house when I was a year old weren't actually caused by her inability to understand the basic principles of how Yale locks work.