The crime often called "involuntary manslaughter", or simply manslaughter in the second degree, is
when, with criminal negligence, he or she causes the death of another
The standards for "criminal negligence" as well as "recklessness" are spelled out here. The first term is defined as:
A person is criminally negligent or acts with criminal negligence when
he or she fails to be aware of a substantial risk that a wrongful act
may occur and his or her failure to be aware of such substantial risk
constitutes a gross deviation from the standard of care that a
reasonable person would exercise in the same situation.
You can elaborate the above scenario with some details to make this be a criminally negligent act, but I assume the intent is to have this be a tragic accident. So for example, I assume that she did not see the fireman.
The law does not require you to die in a fire in case there is a remote possibility that you could injure another person in the course of saving yourself. Unless you add some evil intent on the girl's part ("I don't care if I land on that fireman, that's his job"), a reasonable person would act likewise and save their own life.