Why jail women at all?

I've noticed increasing concern among UK media column writers over the past year about the situation of women in prison, with a clamour to reduce - if not eliminate - the practice of sending women to jail. A good example is this column from Eric Allison in (where else?) the Guardian, late last year: "Women are dying in jails they should not have been sent to":

Many female prisoners are mothers and primary carers. Every year, around 18,000 children are affected by their mother being sent to jail. As women are usually the main caregiver, many end up in care. We can only guess how much that adds to the anguish of mothers behind bars.
A compelling argument to be sure.

Let us turn to the case of Eunice Spry from Gloucestershire, who was sent down for 14 years at Bristol Crown Court in 2007:

Judge Simon Darwall-Smith told the devout Jehovah's Witness that this was the worst case he had come across in 40 years.
Passing sentence, he said: "It's difficult for anyone to understand how any human being could have even contemplated what you did, let alone with the regularity and premeditation you employed."
As punishment for misbehaving, she would beat the children on the soles of their feet and force them to drink washing-up liquid and bleach.
I'm sure Eunice Spry's children were affected by her being sent to jail, but I'd imagine it's more along the lines of thanking God that she was finally kept away from them.

Her defence brief did his best to mitigate, but had something of an uphill struggle:

Mr Mitchell also revealed that Spry had needed protection in prison following her convictions and it was a "particularly unpleasant" place for her.
To which I'd be minded to respond "Et alors?" I hadn't realized before reading the detailed verdict that she was also convicted of "Intimidating a juror or witness or person assisting, or who has assisted, the investigation of an offence" - this is not just a woman who made a few bad choices.

Spry was of course eligible for parole in April 2014 and (of course) was released on schedule - the 14 year imprisonment sentence was reduced to 12 years on appeal.

There's certainly an argument that people are being sent to jail for crimes which are not obviously harmful to society - for example, possession of substantial quantities of narcotics but no obvious intent to supply outside their circle of dysfunctional friends - but let's not special-case women in this argument. If we are serious about gender equality, we should apply the same standards to the decision about jailing a father that we do about deciding to jail a mother. Otherwise we're perpetuating serious inequality in the application of the law to men and women - and isn't that something an enlightened society should want to fix?