A lot of vets are spaying earlier than 6 months now...I've seen several that start at 16 weeks (and even younger). But London would have been too small at 4 months. I do think $650 is expensive for a spay by itself, but if it included teeth extractions, a teeth cleaning, bloodwork, and an overnight stay then it's reasonable. Honestly, expensive to me but I'm assuming the cost of living is higher in New York City than Texas.
Yes, she can have her dewclaws removed. I recommend it because they can tear on something, causing her more pain then just having them removed to begin with. She'll already be on pain meds for her spay and be resting and recovering for that so she's not going to be in much more pain from having her dewclaws removed. Definitely find a vet that will do it. I can't believe the wouldn't do it
So far as staying overnight, I think it is okay to leave them overnight as long as they have 24-hour staff monitoring them constantly. I'm just not okay with staying overnight if no one is there to watch them. The person whose dog had complications brought her home because no one was at her vet's office overnight. She said her dog would have died there because no one was there. So yeah, when no one is there to watch them, no way would I leave my dog overnight.
Hha - $45 must not include any pre-op bloodwork or pain meds. It is VERY important to get bloodwork done when anaesthesia is involved....in most cases, the dog is fine but there could be something going on that you don't know about and the anaesthesia could kill them