You're right, I suppose there are some possible sources for a hefty gift of diamonds to mark the Jubilee.
Sadly, it's been a few years since I've wandered through Cartier or Van Cleef & Arpels shopping for a new tiara or diamond necklace <wink>, so what might that go for these days? I mean, let's say I wanted to commission a gift for the Queen's Jubilee, something on the scale of the Vladamir Tiara, or Queen Victoria's diamond necklace and earrings (the fat set the Queen wore at her coronation). Would it run me £1 million? Two? Five?
If the 759 extant hereditary peers in Britain each threw in £5,000, that should do it. If the several hundred living life peers joined in, they'd each only have to throw in maybe £2,500. Or, if every living Britain threw in 8p, it could be done.
Heck, there are over 7,000 members of this forum alone. If we each donated £5, we might be able to get her a matching bracelet or broach. She might name it the "Ally Pally Broach".