Mistee - dont exercise if bg levels are over 13 - otherweise if you have good control over your diabetes and have good bg levels exercise will be beneficial, doesnt have to be strenuous, any movement is good and better than doing nothing.
Be careful though, you are only just recovering from a gallbladder operation, you shouldnt be going to the gym just yet. But walking should be ok, as you say you are a bit out of practice so my advice would be that you start off slowly and build up from there.
All the best to you x