Poinsetta,
I will pray.for your Roxy.
I'm not giving veterinary advice, but some vets give vitamin B12 to dogs when they are brought in while they examine the patient and perform diagnostics.
The best form of B12 over the counter is the methocobalamin form. It's normally called sublingual or under the tongue. When it's swallowed, the absorption rate goes down.
It's sweet and tasty, so it usually is swallowed. It can be moistened and as a paste, smeared on the gums and cheeks.
I hope it's Roxy recovers quickly.