Okay, I spent some time checking Wowhead and thinking back to my experiences, and I think I have a non-PvP, mostly non-"dungeon grind" progression path you can use.
I've also added a citation where I've been able to confirm with Wowhead the zone is spider-free: (c) for spider-based critters and (b) for spider-based beasts.
1-60: Azeroth Proper
From levels 1–10 do Eversong woods as you've done (b, c). And you're right to go to Azshara from 11–20 (b, c).
For 20–25, you can't escape spiders: every zone for the level range (Ashenvale, Duskwood, Hillsbrad, and Wetlands) has tons of them. I'd try to milk Azshara as long as you can, then move to Northern Stranglethorn shortly thereafter. If that doesn't cover it, you'll have to do one of the two dungeons—both spider free—for this level range:
- Gnomeregan (b, c)
- Scarlet Monastery (b, c)
If you do go the dungeon route, use the Dungeon Finder tool: getting to Gnomergran as a horde is a bit difficult, and a trip to Scarlet Monestary will require going through Tirisfal Glades, which does have spiders.
Northern Stranglethorn is the only zone in the 25-30 level range that doesn't have spider-based beasts, but it has spider-based critters all over the place. (b, c). If the critters are a problem, you'll have to do a dungeon again. Your only option in this case is Maraudon (b, c).
For 30–35, Southern Barrens is spider free (b, c). Like Northern Stranglethorn, the Cape of Stranglethorn is free of spider beasts, but not spider critters (b, c). Desolace is okay if you stick to the mainland, but an island off-shore has spider critters (b, c). Avoid the Hinterlands like the plague, though.
For 35–40, Feralas is the best bet (b, c). Dustwallow Marsh is infested, and Western Plaguelands has a nest of them to the north. Keep in mind Feralas has Silithids to the south, however.
Choose Thousand Needles (b, c) from 40–45 (more Silithids at the south end of what was once the Shimmering Flats though), then either Felwood or the Badlands for 45–50. I'd personally opt Badlands as there's less green stuff that could be mistaken for a creepy-crawly.
For 50–55 it's Un'Goro crater (b, c). You'd think Winterspring would be a sure thing with all the snow, but Blizzard had to go and create snow spiders. Like Feralas and Thousand Needles, there's a Silithid infestation towards the south if that isn't your bag.
Rounding up the old world from 55–60, it's a bit of difficult one. Blasted Lands has spiders, but your alternative is Silithus. Silithus. You can start the Outlands at level 58, so do that. From 55-57, either finish up Un'Goro or do another dungeon: Blackrock Spire (b, c) is your only spider-free option for this range.
Avoid Terokkar Forest and Blade's Edge Mountains at all costs: they're swarming with spiders. Otherwise, you can follow normal progression:
- From 58–61, do Hellfire Peninsula (b, c).
- Then sashay over to Zangarmarsh from 61–64 (b, c).
- From there, go to Nagrand for 64–67 (b, c).
- Finish up with the Netherstorm (b, c) or Shadowmoon Valley (b, c) from 67-70, or just head straight to Northrend at 68.
In Northrend, you should be mostly okay as long as you stay away from the dungeons, which have spiders in them (especially the Nexus, Naxxramas, and Azjol Nerub).
- From 70–72, choose Borean Tundra (b, c). Howling Fjord is infested to the north.
- From 72-75, go for Grizzly Hills (b, c). Dragonblight has the Nerubians, and Zul'Drak has cobwebs everywhere on account of all the undead.
- From 75-78, head to Sholazar Basin (b, c).
- From 78-80, skip Icecrown as it has some spiders and instead focus on Storm Peaks (b, c). The hit you see for the Storm Peaks is just a rare spider that appears in the mountains that separate the zone from Zul Drak: you won't run into it in normal questing.
If you want to avoid spiders, Cataclysm is not a nice. Only two zones—Mount Hyjal and Vashj'ir—are spider free, making it next to impossible to get to 85 without dungeon crawling. So, I'd suggest doing
- Stretching out the Storm Peaks as long as you can
- Mount Hyjal (b, c) and Vashj'ir (b, c) from 80-83
- Any of the dungeons (they're all spider-free from what I've seen) until 85
85-90: Mists of Pandaria
For Mists of Pandaria, you're directly in bad luck: Jade forest has spiders when doing the jade serpent questline and right after reaching Dawns Blossom, now, you normally reach level 86 around the time you're ready to transition to Dawn's Blossom from the Hozen part.
After that, you need to ride manually from the Hozen place to Valley of the 4 winds. You will start to encounter spiders during the Halfhill quests, so once you reach that, you can head over to the Krasarang wilds quests. there are no spiders during the quests themselves, but there is a whole bunch of them at the far east end. there are no spiders during the hidden master questline.
Kun'lai summit and townlong steppes are mostly safe. Don't even think about Dread Wastes: you need to deal with them during the very first 2 quests. However, there's a tall wall next to the spider nests. In theory, you can ask your girlfriend to place her character on top of the walls, send her to another room, kill the spiders yourself, skin them (to get rid of their corpses) and then let her quickly enter the area. there are critter spiders, but not much you can do about those except polymorph them with the crittermorph glyph.
I could link you the relevant WoWhead pages. However, early on, there was a bug where certain spiders would get evade bugged and follow people to other zones. these spiders show up all over those zones, but aren't actually there (they're in an optional dailies area in the max level zone), just polluting the data and making it unreliable.
90-100: Draenor (BETA, INCOMPLETE, marked as spoiler)
It is currently somewhat early to discuss the spiders in Draenor due to the relatively low data population on Wowhead. Searching through quests and mobs, I find a small group of spiders in Gorgrond, and a number of quests involving spiders in the south of Talador.