You need to bear in mind a couple of things, Canary:
1. Although failing to stop and/or report following an acciden does carry a maximum of six months custody, onlt the most serious would be considered for a custodial sentence. The normal starting point for the most serious category is a "High Level" community order. Full details on page 137 of this document:
http://sentencingcouncil.judiciary.gov.uk/docs/MCSG_%28web%29_-_October_2014.pdf
2. When deciding a verdict or a sentence each member of a bench of three "lay" Magistrates has an equal say in determining the outcome. The Chairman (who in this case was female) has no more influence than the other two. Furthermore, unless it is impossible to achieve, the Bench is always composed of two JPs of one gender and one of the other, so there would almost certainly have been at least one male Magistrate party to the decision.
Your assertion that female Magistrates are gullible and soft is without foundation. If you observe the work of Magistrates in their courts (rather than rely on a single report of a single case) you will see that Magistrates of both genders exhibit different qualities but all are bound by the sentencing guidelines. Loking at the very brief details in the report (and the Magistrates would have had much more detail and would almost certainly have had the benefit of a detailled "pre-sentence report") this sentence does not seem outside the guidelines. Custody is by no means a certainty even for the most serious examples of this offence.