Wow, I'm only just catching up on this thread!
Glad you got Biscuit to the vet and that they are looking after her!
I can't tell you how similar Biscuit's story is to Monster's story last week (Monster is my Budgie). We were going to opt for a Suprelorin implant to completely stop any future egg incidents as this is also Monster's second eggbinding problem in the last month. After the x-rays and contrast x-ray study we found that Monster has... complications though, so unfortunately she is no longer a candidate for the implant.
Have you discussed the implant with your vet? They last for 9-12 months and my vet has placed them in birds as small as Budgies with great results. My Dende (who is 85g) has the implant and she is doing very well!
My vet showed me the series of x-rays and she also pointed out that Monster's bones have started to become very dense because they are absorbing as much calcium out of the body as possible. This is the sign of a bird that has been in breeding condition for a long time (or chronic egg layers), which makes them more susceptible to eggbinding. I'm just mentioning it because you said your vet mentioned Biscuit's bones as well. I'd never even heard of this until yesterday when I went to the vet for Monster's follow-up vet visit.
I'll keep Biscuit in my thoughts! Come on little girl! We all want you to get better quickly!