Okay, I'm really really late on this one, but I recently started watching XY after being away from the anime for a long time (it's so pure and such a good anxiety soother, aaaa)...I just got to that episode, where Ash remembers Serena and there's the flashback to camp. It was honestly more endearing to me than I was expecting :D
I mean, when little Serena was lost in the woods and panicking, then hurt her leg and started crying for her mother and regretting going to camp...I just could really put myself in her shoes. :( I can see why Ash stuck in her memory so much, showing up in such a bleak (to a kid) situation and not only helping with her injury, but acting as her companion and helping her calm down. Then later in the episode, she helps him out with the Rhyhorn thing...I think they make an excellent team. :3 (Also, wow! Serena really held onto that handkerchief for a long time. :O XD)
You haven't seen anything yet involving those two. Ryhorn race in Episode 7 was just the beginning. I'll give you a list of Episodes to watch. Not all are mandatory but they all have their own Amourshipping quirks.
Episode 13 with Ash battling a Fairy type for the first time(Sylveon ironically enough) where Serena gets concerned that Ash might be "taken away"
Episode 21 involving Pokevision
Episode 26 where Miette is introduced
Episode 31 wherein Serena gets a sentimental photo of the group(particularly because she's close to Ash)
Episode 37(Cave of Mirrors)
Pokemon Summer Camp Mini-Arc(39 through 42)
Episode 53(Serena vs. her mother wherein Ash helps motivate her to win)
Episode 59(Self-explanatory)
Episode 60(particularly the end)
Episode 73(more so because it introduces Sawyer and has one of my favorite scenes in it)
Episode 78(optional filler but its a Pikachu movie...)
Episode 80(Miette again with an infamous Bonnie scene)
Episode 89(Eevee for the win!)
Episode 90(Shauna and an infamous Amourshipping scene)
Episode 105(XYZ 12 and of all Amourshipping Episodes, this is #2 by far)
Episode 109(XYZ 16 Serena's Final Key)
Episode 112/113(XYZ 19/20. Master Class Episodes)
Episode 115( XYZ 22, Mrs. Serena Ketchum by alot of Amourshippers)
Episode 120/121/122(XYZ 27/28/29, Snowballs be flying, true feelings come to surface)
Episode 138(XYZ 45, last battle with Ash)
Episode 140(XYZ 47, infamous #1 Amourshipping Episode)
Also Episodes 14, 29, 47, 50, 64, 72, 83, 85, 91, 95(XYZ 2) and 101(XYZ 8) are optional but have good Serena moments. Strongly recommend you give XY&XYZ a solid chance. It takes awhile to get going(particularly with regards to Serena) but it quickly makes up for it from say Episode 80 onward. Not to say the Episodes prior to it are trash(they're not) but plot-wise with regards to Serena, it speeds up considerably as her performer arc is done by Episode 113(or a span of 34 Episodes if you include Episode 80).