I had back to back maternity leaves with my 2 children - I went back for 3 months in between (I took the full year and then had several weeks accrued holiday, there are 18 months between my children).
The job I went back to originally was part time, 2 days per week and I suppose as both I and my employer knew it was only for a short time it kind of worked.
Now I have been back for six months, again 2 days per week, but in a different role... and it just isn't working at all.
I have been put into a different team, doing a different role (I did this job at a more junior level years ago and so I am having to do some work to get me back up to speed but I am getting there). The team basically consisted of one senior manager and his assistant before I joined them. The senior manager wants to retire in a couple of years and is basically winding down - he has no interest in winning new business and just does what he has to do. Our bosses shipped me in a) to cover the days the senior guy doesn't now do and b) to bring in more business. I have brought in some new work which is good but the senior guy and our assistant do the bare minimum on it - pretty much everything just sits there until I come in. I am expected to work on his matters - in fact I feel he leaves me all the crap to do (difficult conversations, things that require a bit of thought).
Today "our" assistant just completely refused to do something I asked her to do. I had to turn the work away as I am on annual leave this week as my DS has half term from pre school and it wouldn't be fair on the client to leave it until next week.
I end up having to check my emails all the time and even go in on evenings/ weekends when I have childcare to get on with work.
My DH tells me to go to my bosses but they are scared of the assistant! She cries discrimination at any problem and is a really difficult character - plus my bosses are really weak and never back anyone up. I have been treading on eggshells around her since I have been back and have been doing everything myself to avoid her - the task i asked her to do was simple but she just said she "needed training" as I use our case management system and the senior manager doesn't (that is a whole other thread). They are basically a law unto themselves and I feel like I have been shunted into their "team" and they hate it.
I am not sure where to go from here? I can't rock the boat too much as I am not quite up to speed to do the senior role and I don't want to increase my hours for another year. Plus, I doubt the assistant will want to go anywhere - literally- there was an office move whilst I was on my 2nd maternity leave and she refused to change desk (it is by a window) so she now sits with a completely different team whilst her manager is on a different floor 
and she was allowed to get away with it!