Cracking up at the thought of someone commenting on how Guda hasn’t aged in years and they just chuckle nervously and “yeaah I think I died and accidentally summoned myself as a servant actually but I’m trying really hard not to think about it.”
Do hear me out: at the beginning of fgo, Guda tried to save Mash, and upon failing, resolved to hold her hand and give her a peaceful death. That’s pretty heroic to me, or at least, to Mash, it must have been. Coincidentally, at that very moment, as humanity is being incinerated, Chaldea is pretty much what’s left of humanity. So, let’s be generous and say there were a hundred people who survived in Chaldea. Mash represents 1% of Chaldea. Mash effectively represents 1% of humanity at this very moment. That’s a lot. (I think 1% of the world population rn would be more or less the population of France) 1% of the world population believing/remembering you as a hero is more than there are people in the world rn who know who St Martha is.
Conclusion: Guda could have very well entered the Throne of Heroes on the basis that Mash believed them to be a hero, and immediately afterwards be summoned by Mash, because I mean, what better catalyst than someone’s corpse?