My wife is being told that her postion changed from part-time to full-time after mat leave, is it legal? [BC]

As the title says, my wife is returning to work on sept 1st. When she reached out to her employer, hr responded saying that her position had changed from part-time to full-time with the same compensation. They're asking if she's willing to take the job if its full time.

Is this legal? If isn't what should we do about it?

Any advice is greatly appreciated it!