How was your return to work? (long rant)

Am unhappy since I've returned back to work.

I used to work full-time before going on maternity leave.  I work in a large organisation as a Secretary/Typist and there are three of us in the pool.  I've returned at 15 hrs a week, and there is not enough work to keep us all busy. 

The boss is one of those 'smile through their teeth' kinds of women I don't trust.  She seems to favour one of my co-workers with the more important and/or rewarding tasks, while I am often shuffled all over the place to do menial tasks.  I get treated like a temp.   Wonder if they think I popped out my brain at the same time I had my daughter!    My self-confidence is eroding away to nothing.  We also seem to be heavily micro-managed, ie everything has to go through that boss. 

To make matters worse - this particular 'co-worker' who was once my equal now seems to feel superior enough to tell me what to do!  It's only happened a few times - but she's not my boss and I really need to nip this in the bud without blurting out something rude.  Really need suggestions???? 

I almost cry when I look through my CV.  I used to be a Legal Secretary, very busy, professional and felt respected; managed the IT network at a few places, and have generally been a 'go-getter'.     Now after a working at this place, my computer skills have really declined as I'm not getting to use them.

I get the feeling that my boss wouldn't be all that bothered if I left, as there isn't that much work.  If I got another job it would be a huge hassle to rearrange my daughter's care (she has a brilliant carer who may not be available if I were to change my hours).  I feel like I'm against a brick wall here. 

We don't depend on the money from this job.  I do like to work outside the home, but I don't like being treated this way either.   I find myself feeling anxious about going to work, and ruminating about it all the time.

Maybe someone has a different angle on this?