Well, it’s been a month and I realized the original postulate was innacurate, explaining why I didn't go anywhere with this.
Forget about everything that was said before. Shop 3 is not a variation of Pink’s leitmotif, but it’s in "Cutie Mew Mew Magic" in 4/4 (1:49-2:05, if you want to compare both themes), making it a possible part 3 of Pink’s motif (or the great comeback of "Shop 3").
Check this discussion for further details: https://undertale.wiki/d/t/flowery-in-running-sky-quiet-glade-and-sunset-of-seven-suns-motifs/8127/8