It is suitable for dogs with pancreatitis. As mentioned in one of your other threads, the pancreas might be damaged and then unable to make the Intrinsic factor to digest the tablets. So you need the right tablets containing it.
Injections of pure B12 (red stuff) at the vet works immediately in the blood stream. Then injections once weekly for six weeks followed up once monthly. Obviously some vets charge silly money for a£10 injection so you are fine to use pills, which are slower because they aren’t always well digested. The protocol is one 1000mg pill daily. When an improvement is seen it can be reduced to weekly. It is a harmless supplement, excess is wee’d out.
My personal experience of low B12 is positive. You can feel the injection working in hours. Then when I guessed my levels sank (losing car in car park, inability to add up money, forgetting words, driving on autopilot to the wrong place) I went back to a mean gp. He wanted to refer me to a memory clinic! I insisted it was low B12, as it was at 200, and rock bottom is 190 ish, normal is over 300in UK or 500 in Japan. So I refused his offer and took the tablets daily as described. I returned to normal in a few weeks. I still take about three a week,.
You can get liquid B12 to squirt under the tongue (sub-lingual) from Holland and Barratt. It s supposed to soak into the tissues, but I wasn’t impressed by it.
Obviously with an elderly dog, it could be something else, but I agree wholeheartedly with you trying something harmless that could help. I don’t think a vet would be much help without doing a blood test, which would upset your girl, and cost you £60.