Fairy Tail 100 Year Quest: Chapter 103 Revisions

[UchihaSlayer96]

The point isn't only that she uses the spell, but the fact she remembers the events of that arc, which I think would allow it to be considered canon.
The filler arc is where she uses the spell together with Yukino and Hisui, and learns that the latter is a Celestial Spirit mage, all elements that return in this chapter explicitly because Lucy has memories of that.

This means that either the arc is canon, or we assume Lucy went through some unknown event that led her to cast Gottfried together with Yukino and Hisui for some reason, otherwise she wouldn't be able to remember it and summon copies of Yukino and Hisui to help her. (and the previous page is all about her tapping into her memories of past events).
I usually don't like to pull the "Occam's Razor" card, but the most logical explanation is that she remembers the filler arc because it happened, instead of some other unknown but similar reason.

It is also supported by the fact that the manga is used to make fillers canon, so it wouldn't be anything new.

I was initially going to agree with Arc, but Saman's explanation, as well as some of the others' arguments, turned me around.
So yeah, I agree with the OP.

 

[DemonGodMitchAubin]

Well that's 5 staff in favor of the OP, I shall apply the changes and close this

Now we need to consider what the Eclipse Arc being canon means