The "else" could be Jules or Trey or someone new passing through.
Keep in mind that these birds have really good eyesight, from the easternmost edge of the West Winnipeg territory, you can see the Radisson - and with a spotting scope you can see birds flying around the Radisson. If we can see that then so too can the peregrines. So if Jules knows Ivy is back (maybe she does, maybe she doesn't) she could conceivable come downtown to investigate. The last time he pulled this visiting-with-Mom thingy, it was the first year that Jules and he were a "pair" even though they didn't nest out west. To be clear, I haven't seen Jules downtown, its just a possibility.
As for Trey, haven't seen him yet as everyone knows.
As for someone new, peregrines pass this way alot in the spring, if Trey doesn't return and Princess won't mate with Ivy and Princess manages to hold the territory (male-female fights aren't common, combat tends to be gender specific), a new male passing through may be exactly what Princess will be looking for ...
We will just have to wait to see what (or if) the "else" ends up being!