Thank you so much for all the information!
I am not at my mothers right now, so I can't check or measure the glasses, but I'm 99% sure they are crystal. Not certain about height though, but I think they are the short type of sherbet glasses.
I have checked ebay and found nothing yet, but as you say, there is quite a bit to go through, especially when you don't have a maker OR a pattern.
Also not at all sure about London, but I don't think they are bought in Italy. I wish I could ask my mother, but I want to get them for her as a present, and that would spoil the surprise.
So I'll keep looking and I'll try sending replacemants an email with pictures