Yes, you're right, I kept thinking Edward was born in 1281, then checked it was 1284. His sister was born in '81.
Well, that's a marriage that would tighten the screws on Philip. Secures a vital ally in the Low Countries and ensures the continued vitality of England's lucrative wool trade with those Flemish merchants. Blanche of France though was born in 1282, so she might still be a viable match for Edward of Caernarfon, only a 2 year difference there.
I mean, I see that Philippa was betrothed to EoC here in 1294 and was later imprisoned in OTL by King Philip. Now, I'm just working off the POD that I proposed (a surviving Eleanor of Castile encourages her husband to let Balliol be and instead build him up as an ally by marrying his their daughter to his son), so after this, does this engagement still happen if Balliol is crowned I'm 1282? This changes circumstances here. Philip would rather not see himself fighting a war on 2 fronts if he keeps meddling and knowing that England and Scotland have renewed their up to that point historical alliance, Philip knows that if he antagonizes Edward or his allies, he will have Edward's undivided attention. And this version of Edward is the sharper, more diplomatic version of Edward with his beloved wife still around getting the last word in. So I think Philip doesn't drive Guy into Edward's arms as quickly as he did in OTL and thus, Philippa remains a viable and strong marriage candidate, arguably a leading candidate at this point, just not automatically betrothed.