teaching over timetabled hours

[deluxevegan]

So, here goes... I work in a college and teach A2 and AS English along with a part time colleague, we are at the a 3(her)/2(me) hour split with AS and the other way around 3(me)/2(her) over the course of the week. . This colleague has been an absolute nightmare since I began working with her. She has bullied me, been rude to me while our line manager did nothing because she is afraid of this colleague. because of sharing most my classes with her my timetable this year has been really difficult, i teach 6 lessons out of 7 on both Thursday and Friday! I requested for a change but nothing was done about it so I sucked it up and taught this 23 hour timetable.
Now, that A2 and GCSE have left, I am teaching 6 hours a week and she is teaching 9 hours a week (we have three AS classes and she works Mon-Wed) and has now requested for her Wednesday lessons to be transferred on to me as 'it is not fair' that she teaches 9 hours.

Can my college do this? When I have spent the year teaching 23 hours a week and have fulfilled my timetabled hours can I be asked to teach someone else' class now that we are the end of the year and she is part time?

Please advise, this is making me really angry and frustrated.

It's not uncommon for timetables to change during gained time to reflect staffing changes.
In 11-18 schools, I've certainly picked up some extra hours some years when a colleague has gone on maternity leave and school (somewhat understandably) don't see the point in having 8 Year 11 teachers, some also taught Year 13, and then paying a maternity cover for 4 weeks before the summer.

In your situation, I'd be concerned that there's no justifiable reason for the change other than the colleague flouncing. Your manager really needs to get a handle on this colleague as colleagues who throw throw weight around are toxic for the team.