I was struggling to see the logic of her taking abortion drugs too, until I realised that she did this while her husband was away. So what I imagine is
she got pregnant, assumed it belonged to the man she was having an affair with
it was too late to terminate
she concealed the pregnancy from her husband
she took the abortion drugs to induce labour THAT DAY so baby would be born while her husband was away
she had the baby which was either stillborn, murdered or given away
Of course she should be jailed. Prison is not just to serve a purpose for the offender, it is to make it clear to EVERYONE that laws are laws for a reason and you can't just break them if you feel like it. It is not legal to take abortion drugs except under certain circumstances as mentioned above, so presumably they have prosecuted on that basis because they do not have a body to prove a murder charge.
in terms of the abortion act, abortion is permitted up to 24 weeks - this was last debated in parliament in 2008. If there are serious foetal abnormalities, abortion can take place after this time. Here is a link to the Royal College of Obstetricians and Gynaecologists fact sheet about Cleft Palate and late abortion - although it is not as clear as it could be it does seem to show that they are supportive of this law/policy being continued rather than changed.