It's not important what Sandra Jansen thought, or who is running the Alberta PC party, or what the media says about floor-crossing.
There are really only two question here.
In the past, have the Alberta NDP expressed a negative opinion of floor-crossing? Yes they have, including the current Alberta NDP leadership.
Did they abandon that position the first time they were the 'receivers' of the floor-crossing? Yes they did.
If any here think no one is going to use this little event in the next Alberta election campaign, think again.
The Alberta NDP could have taken a principled position of supporting Sandra Jansen in her battle with the PC troglodytes, and either accepted her into caucus at the next election, or after a by-election (if Jansen chose to resign and run in one). In the meantime Jansen could have sat as an independent, votiing with the NDP. Principles upheld, and everyone happy, even Jansen's constituents.
As far as the expense of a by-election, I'll just point out that by-elections are held all the time, for a variety of reasons. One more or less isn't going to make a lot of difference.