I think what stands out to me is the only time the Doctor has laid eyes on her is when she was Ambulance, an AI. What i think about is the fact that The Doctor has always said he would recognize another Time Lord/Lady…but obviously not as an AI.

I love the idea she's actually the Memory Tardis in Human Form and using Ruby as an anchor. Some side lines the goldtooth was picked up by someone with very red nail polish Kate was wearing the same in the latest episode and was on the roof after the game ended. RTD is already busted he said Susan Twist was just used because she was good and available but Ruby now mentions about seeing her before. Is Susan the woman who leaves Ruby at the Church for the Doctor to find, RTD said the timeless Child would be covered = the Doctor finally knows all about the past and Ruby finds out she's been created to help this happen.

Apart from Mrs Merrydew in Wild Blue Yonder, all of Susan Twist’s scenes had Ruby in the scene with her. - She heckles Ruby in the pub in the Christmas special. (Present time Earth). - She appears to Ruby in Space Babies as one of the crew, when Ruby’s looking through the files. (Future time other planet). - She gives Ruby and the doctor a cup of tea in The Maestro. (1960s Earth). - She is the face of the ambulance in Boom. Revives Ruby. (Future time other planet). - She has a full conversation with Ruby in 73 Yards. (Present time Earth. Alternative timeline. Alternative timeline erased at the end of the episode). This makes me think Susan Triad is a Time Lord. And the twist could be she’s going after Ruby instead of the doctor. It would explain why she doesn’t make herself known to the doctor. But still keeps an eye on Ruby when the doctor isn’t looking.

There’s always a Twist in the end.

Whomever she is… the reveal should be worth it.

I feel like she sent playing games here. I think this version definitely doesn't have any secrets. she's just a walker going about her business. Maybe Susan Triad is thrown back in time.

What if she's like Clara, scattered throughout Ruby's timeline instead of the Doctor's?

The Doctor's Granddaughter? That would be a hell of a Susan Twist! (He does mention her to Ruby in 60's London)

I suspect Susan Twist is a distraction---albeit a fun distraction--from the real mystery this season: Mrs. Flood.

I don’t know how or why, but this appearance convinced me that her appearances are random and unconnected and not intentional, like none of these Susan Twists know that there are others out there. I could be very wrong, but there’s no evidence to suggest there’s any plan here and the innocent walker really cemented that for me, like she was truly minding her own business.

I think Susan Twist’s character has something to do with Mrs Flood but I’m not sure what. Perhaps they are the black and white guardians?

She could be Ruby's mum

I think Susan has a plug in Dr who’s casting 🧐

At this point, does anyone really give a toss?

I think Susan is “the one who waits”.

What if the recurrence of the character in various points of the Doctor and Ruby’s adventures is some sort of punishment of the character, a consequence of being defeated by Ruby and the Doctor in the season finale?

Was she only cast because of her name?

Imagine russell is just playing with fans and indeed she is just being reused as an actress nothing more

I just think Susan Twist has a REALLY good agent!

She’s an impossible girl of sorts it will become to happen but Ruby is the real twist, she dropped her self off, she’s a baby that comes into being because she is a living god, no need for Mary in who

Susan Twist = Susan, granddaughter of the doctor. I know, it's such a simple twist, but this is Disney now, so the target audience is (american) children, and they are no good with complex stories or twists.

oh so cool! Wait, NO, it's not. I don't care. Cancel this show or replace RTD and never bring MOffat back either.