I think its pretty clear that Aran'gar was holding saidin if she gasped. It's a recurrent reaction we've seen when a channeler is suddenly shielded and loses their connection with the Source.

I also don't think that strength is a primary determinant here. Graendal is immensely skilled. Aran'gar was facing the window and unprepared. We know that channelers can shield one another if they are of equal strength. IMO Graendal is stronger or equal to her and overwhelmed her with sheer speed and surprise. Whether she used the angreal is difficult say, but the author usually mentions if a channeler pulls through one.

We also don't know whether she shielded Delana and Aran'gar at the exact same time, or did it quickly and sequentially. She's certainly fast enough to pull off two shields that look like a single weaving.

Anyway, I don't find it a big stretch for a female Forsaken to shield a male. I think it's been a well established fact that the females are close to the males in strength, and Graendal is near to the top of all channeling strengths.