As a general rule you would feed a puppy twice a day until approximately a year old, although some people do it all their lives. However, if the pup is starting to leave some or all of one of her meals, then depending on the size (breed) I would start to reduce one meal and maybe substitute with either a couple of biscuits or a drink (such as goats milk).
If it is a large or giant breed, you should try to keep the second feed going by using something more tempting.
Mine always have a bowl of dried food down all the time so they can help themselves if they get peckish, and often have a bit of a breakfast snack. They still all sit and wait for their main meal, although it consists of the same stuff, plus a small amount of tinned meat or tripe or chicken.