is there a higher chance she will miss again if mated on her next season and what factors cause a girl not to fall pregnant if a well proven stud is used?

I would say no (having never had a bitch miss twice in a row), though speak to me in two months time, as just trying again after a miss.

As to why a bitch may not get pregnant or carry to term.  Hormones out of balance/low can cause them not to ovulate, not enough to maintain pregnancy.  Then there is the possibility of infection, trauma, or something causing abnormalities in pups.

The most common reason for a miss is wrong timing bitch ovulated earlier or later than the timing of mating.

I don't think that a miss is necessarily followed by a second.  I had my first miss last summer - came as a surprise because it hadn't happened before!

I think that I must have left her too late, and she was taken back to the same stud on her next season.  I have now got the show pup that I wanted!