The animation looks like it's from 7...yet there's no place I can think of where a scene like that would take place.
I'm 80% sure that's Littlefoot's tail, but let's say it's not...maybe it's the tail of aother dinosaur she passed while going to see if Petrie was alright in 7? The background seems to agree with that scene, but her expressio and position doesn't; and it's not at the end, cause the background doesn't seem to agree.
It's definitely in the great valley, so that rules out movies 1, 4 and 9---she has no night scenes in the valley i those movies.. And the trees have leaves on them so that obviously rules out 5.
It does't look like the background for where they gather in 3, but there's a slight possibility that it could be during when they gather in 2.
Her only night scenes in 6 are by the fire pit, and it's obviously not there. It doesn't look like it's snowing, so that crosses out some options for 8. Could it be the scee at the beginig where she can't get to sleep? Unlikely, espicially since Littlefoot's not there.
10 it's not, seeing as Littlefoot isn't there during her one night scene in the GV; nor is she near any random adult dinosaur.
11 definitely has night scenes with her in the GV, and so does 12---but the animation does't look like those films.
So here's where I'm at:
Judging from the aimation in the pic, I'm gona say it's somewhere between LBT 2-7.
Judging from the night scenes she gets in the (fully grown) GV in those fims, it's either 2, 3, 6 or 7.
Judging from the background, it's either 2 or 7.
And judging from the fact that it's most likely Littlefoot by her, it's I'd say it's either at the end after the rainbowfaces depart, or during their meeting in 2, probably when they're looking down at the GV.
And I'm going with the latter.
One more thing: their is a slight---and I do emphasize slight---chance it tkes place durig "No one has to be alone". But from the background I'm sure it's the great valley, as nice as that part of the mysterious beyond looked in 9

So I'm still going with my 2 aswer.
Sorry if that was overanalyzing.