Guppy gestation is generally around 30 days and USUALLY fry will emerge but depending on their environment they don't always give birth. Live bearers have been known to hold and sometimes resorb fry if they feel unsafe or don't have adequate cover in which to release the offspring. It's sometimes also the case that when females hold their fry the mother can die due to infection of dead fry in the womb, though this is uncommon
Your guppy looks close to giving birth. One way to know is you can look for the squaring off shape as shown in this picture
Usually once they square off, they will give birth within 24 hours, usually at night or when the lights are off. However it's not uncommon for guppies to give birth during the day time.