Sorry about the diagnosis. My Pirate has advanced DM, among a host of other health problems. We treat the DM with Metacam, a dose slightly higher than her weight actually calls for, every day. Plus Gabapentin 100mg once a day every day. Gabapentin is actually a human anti-seizure medication, but for some reason it works on neurological issues too. It's also prescribed for chronic pain. My husband has taken it for back problems. It's much more effective for Pirate than it was for him!

Pirate has been on the Gabapentin for about four months now. Before she was falling over, dragging her back leg, unable to lift her back feet high enough to get around even tiny obstacles. A piece of gravel in the yard was enough to make her fall over. She's much steadier on her feet now; can usually get up on her own; she's never going to convince anyone she's 4 again, but she's doing alright for 15!

Might be worth asking your vet about-it's cheap, easy to administer(I throw the capsule in her dinner bowl) and it certainly won't make things any worse.