Bluntness you drew attention to the fact that in five years she has taken maternity leave, sick leave and now has sick children. Why raise the maternity leave and sick leave if they are not relevant?
I'm not sure how you can misunderstand something so simple. But to explain, not one of these, even the last five months on returning to work is an Issue as such intself if contextualised in an otherwise good employee. The sheer volume of absence is the issue. Hence why we are looking at rhe bigger picture.
So The issue, which I and many other posters are making that is in 5 years she has worked approx 18 months, and due to thr age of her children and the year of with pnd, it means most of that work was in the first year, in the last fhree years she has worked a matter of weeks per year. It is now at a level that on any given day there is a fifty fifty chance she will be there. And that has been since her return in September.
This is not sustainable for any business. That is not wrong and yes of course looking at the bigger picture is relevant. That's why it's mentioned.
The employer is not unreasonable. The op is not unreasonable. There is no bad guy here. It's a shit set of circumstances that they all seem to be managing as best they can.
What's been said is when it's at this level, then it's reasonable for the employer to terminate. I don't think even the op disputes that. Due to her personal circumstance she is unable to meet the basic requirements of the job, namely acrually simply turning up two days a week and staying all day.