Exactly. If Dagny has some of Rand's heroic nature, could she also share other traits with Rand as well?
Could Rearden and Galt share traits with someone in Rand's life?

Happily married? Not according to Barbara Branden's memoir, "The Passion of Ayn Rand." The movie has Helen Mirren as Miss Rand. I remember watching the movie as being like watching a multi-car pileup. She's writing "Atlas Shrugged" during the period in which the movie is set.

Thank you

Thank you

Galt represent the ultimate hero in her philosophy and as such Dagny would ultimately be most attracted to that. She states this in the pages that is not what HR or Fransisco don't represent, but what John Galt does represent.

Rearden was a hero in every sense, but he sold out. It was under extreme duress, to save another person's reputation.
Galt did not give in, even under torture.

Was Rand happily married when she wrote AS?
Did personal experience affect her choice for Dagny?

I would agree to an extent. However, to present an idea its totality, as you want it seen, the motivating factors driving the primary characters to their decisions have to be sensible and fully understandable. This is the only tool the author has to have the full meaning of whats being said to be completely understood by readers. Considering Rand was presenting a philosophical point of view I would think this was a primary objective.
I convey this as an author myself. No wasted words. No missed opportunities to deliver your message.

a fictional story and why a character does something???

really???

the story is to present a point of view
and actions are to help with that

I think she and Rearden were drawn to Galt at a deeply personal level. Their relationship was a celebration of that common thread. When side-by-side, Rearden and Galt, She was attracted to the brighter light, the source of the inspiration.

My 2 bits.