Good points and something to think about.
I believe it would (and should) be her income, yes. I also believe she wouldn't have to pay taxes on it, because in Canada income from child support payments is untaxable. (Must be nice!)
So that might work out best for everyone. If she's amenable to accepting it that way, and like you said, this is a large enough chunk of change you'd think she would.
I really wonder if there are other guys dealing with this as well. That's part of why I posted this, in case I can help anyone else going through it. I doubt I'm alone! Many just choose to keep quiet about it, for various reasons, and I can appreciate that.
!LUV