Unless things have changed since I last used the bus...:
- You can't really miss it at Ottawa rail station, it is parked just outside the building, and it is in KLM sky-blue and has "KLM" written on it. You check in inside the station building - they have a dedicated desk which is quite easy to spot.
- It's fairly easy to find at YUL as well, you just walk outside the terminal building and there it is! (From memory the bus stop is slightly to the left of the main door). They usually make an announcement about it on the flight just before you arrive, so just tell your wife to listen out for that.