I'm a not *that* experienced, but my little stimmy is 4 now (just over a meter and 500g) and has gone up a feed a few times. He goes off food for long periods, especially before shedding, but then gets back into a regular routine and has gradually gained weight.
Signs you may notice - she might get nippy, or still be very active after eating. Often if they're full, they will sit in their hide for a couple of days before moving again.
Food usually needs to be big enough that they'll need to dislocate their jaw and get a good stretch going with eating - else its' too small. I think the rule of thumb is about 20% of the weight, or about as thick as the thickest part of your snake. And when they've eaten, you should see a nice swollen belly.
Younger and smaller snakes may eat more often (once a week) but once they get bigger, they may stretch out meals a bit longer. My guy won't eat each week these days, so now I give him 2 or 3 adult mice once every two weeks.
You might like to offer two pinkies before going up a size? It all depends on your snake!
The stickies are a good source of info too - and also look at photos of folks feeding their snakes which will give you an idea for how big to offer. It always looks so big, but the snakes love it!