My Dog Is About 15 Years Old And Has Started Losing Control Of Bowels And Is Throwing Up And She Seems To Be Having Seizures Around Her Mouth Area, She Is Such A Faithful Friend, She Never Leaves My Side. What Should I Do?

She has arthritis and has cataracts on both eyes that the Vet. Says is just because of her age. She is not eating very much and she throws up when she does. Do I just let her continue in this way or should I let my Vet. Put her down?