Relax....
I'm here now.
I'll take care of this.
I don't use smilies but if I did, then I'd use the "rolleyes" now.
LBB, Welcome! Great first post.... really. I've never suspected nor have I seen any posts that suggest Catelyn ever was unfaithful to Eddard... so I'm excited to mull this one over.
LBB, if you've not read through ADWD, then please avoid the rest of this post. It will spoil ASOS, AFFC, and ADWD. I'm also going to throw in some of the biggest theories out there regarding parentage and who is alive and dead... so if you don't want to know these, then stop reading.
I cannot really refute any of your ideas beyond what Imp already posted.
But I'd say that just as we look through Eddard's, Jaime's, and Barristan's POVs and memories to find clues for Jon's (and Tyrion's) parentage, we should look through Eddard's and Catelyn's POVs to find clues for Sansa's true parents. I have not yet reread Eddard's and Catelyn's POVs in this light, but my gut instinct says there is nothing there. Eddard and Catelyn are dead... so who else can tell us of the first three years that Eddard anc Catelyn were together in Winterfell? Maester Luwin, Steward Poole, Ser Rodrik, Septa Mordane, Jory, Jullen, Farlen, Gage, Mikken, Septon Chayle, Lord Karstark, all the Tallharts, most of the Glovers, and half the nobles of the North are dead. Who has this information to give it to Sansa and to us? Benjen? He's either gone, dead, or undead. We suspect that Howland Reed holds the secrets of Jon's birth and that Varys also knows... possibly Littlefinger, Pycelle, Barristan, Connington, and Ashara Dayne as well. But if Eddard is not Sansa's father, who else knew besides Catelyn? Are you going to suggest that she met secretly with Littlefinger? Baelish as Sansa's father is a bit disturbing, but actually semi-delicious since he is now posing as her natural father. Until I reread Eddard's and Catelyn's POVs with this theory in mind, I'll continue to think that Imp is correct... It would dfeinitely be a great surpise, and I honestly don't think that GRRM has set the table well enough for it, so it would pretty much be a deux ex machina moment if it occurred
If Catelyn had bedded another man, I think we might have picked up a bit more of either animosity towards Eddard, an unknown sense of regret, a softening towards Jon, or worries that Eddard does not love Sansa enough. And I don't think we get any of these... She's harsh to Jon... She's frustrated by Eddard's affection to Jon... She's comfortable with Eddard's love to all of her children... And she's only regretful about quantifiable things; Jon, Hoster, Edmure, Lysa, Petyr, losing herself during Bran's coma, her loss of her daughters, and her abandonment of Rickon.
But the biggest problem I have with this theory is the number of bastards... especially surprise bastards... that we'll have in the story. The big one (and probably the worst kept secret on the internet) is that Jon is not Eddard's son. At least half of the fans of the books and the show will not see this one coming when it is revealed... and it will blow them away. The other shocker will be the multiple revelations of the other children of Aerys II, the Mad King. Tyrion, Cersei, and Jaime might all be his children. Okay, so I don't know this for sure, but I think it's true... and if it is, then how many more secret highborn ******* revelations can come out in the last two books? I just don't think there is room for GRRM to use this plot device after Jon and the Lannisters.
Those are the problems I see, but as I said... I've not reread with this theory in mind.
On the plus side...
1. The relationship between Littlefinger and Sansa is already intriguing and this theory would take it up another level or two.
2. Many people expect Jon to be one of the heads of the dragon. If Dany is barren and Jon is her husband, then the third head needs to be female to secure a blood heir to the Targ dynasty. We already know Jon's penchant for redheads. [Sansa could also claim Winterfell if Rickon never comes back. If Tyrion were killed, Sansa might also claim Casterly Rock. If Sansa marries Harry and Harry and Robert Arryn both die, then Sansa might also claim the Eyrie. If Edmure dies childless and the Blackfish is killed, then Sansa might also claim Riverrun. Sansa might be the most eligible lady in the land... forget Asha, Arianne, Cersei, Myrcella, and Margaery.] Soooooooo.... if Eddard is not Sansa's father and Eddard is not Jon's father, then they're not related at all.
3. Mayhaps there are clues in Arya's first POV. Remember she was worried, when she was very young, because she did not look like any of her siblings? She was afraid she was a ******* because she did not look like her siblings... but she absolutely looks like a Stark. Sansa used to always make sure that Arya knew that Jon was not their full brother... she loved to point out that he was a *******.
4. In AGOT, Sansa used to dream of knights and ladies living in fairy tales. She's found out that knights are not what they seem. She's found out that Kings and Queen Regents are not who the tales say they are. She's had all the illusions stripped away... except for the fact that she's not even a lady.
5. Sansa Snow has a nice ring to it.
6. Varys calls his spies little birds. They're orphans... and many of them are probably bastards. Sandor calls Sansa little bird. Sansa is now an orphan... and maybe a *******.
7. SanSan. Years ago, during the heyday of the combination names of celebrity couples, i.e. BenJen, TomKat, et al., I proposed a moniker for Sandor and Sansa... SanSan. Since he's not a knight, since he's crippled, since he's a monster... and now since she's not a lady, maybe they'll hook up. SanSan.
LBB, I look forward to your ideas. If you can find more concrete evidence in Eddard's, Catelyn's or Arya's POVs, please show us!
Edit: What is double D/D and D?