My 1997 isuzu rodeo is randomly hard to start in the morning?

i went out to the rodeo this morning and it kept turning over but wouldnt start. i kept trying untill the battery was running low on juice. i took my spare car to work....my girlfriend about 2 hours later goes out and it starts right up! i asked what she did and she said that she pumped the gas pedal while turning the key and after about 10 seconds it fired right up....it is fuel injected so i dont see how pumping the gas pedal would help?.....what could be the cause of this?