I'm going to give Shadows a whirl this weekend, and for convoluted reasons I have one player that may or may not make it and wont know until the day of, but they were the first person to say yes to the game, so I've grabbed a fifth player who will be the 4th player if the unreliable one can't make it, and if not will be a 5th character.

The PDF is pretty clear about how to cope with only having 3 PCs, but I guess I've got the opposite problem. The obvious solution is to have them play Helga (I don't have the PDF in front of me at the moment, I think that's the name of the NPC that is in with them when they wake up)

I guess I'm just looking for any suggestions or advice from anyone that has run this with 5 people, or ideas for stuff that could resurface in her memories to give her stuff to do beyond go “man that monster is scary, better get away”.

Given she serves to split the party up or make it so that either she or Manny can die, I'm assuming putting sufficient stuff in her backstory to get her exploring the ship should probably suffice (I'm guessing 90%+ of groups abandon Manny anyway). Although reducing the thugs to 2 people and making one of the other NPCs a replacement Helga is an option, it feels like making the groups 2v5 instead of 3v4 reduces the threat posed by the thugs too much. Maybe she could have a pet dog that was in stasis in one of the cargo pods that she wants to go check on, that has gotten out/been killed?
I could also bump the number of stasis pods in each section by 1 and throw in a few more NPCs. I assume that Theta murders the Dr because of who they are instead of just random chance? (It's a bit unclear and the timeline at the start doesn't actually mesh with Casey's character sheet's version of events) so, I could add a second Theta Project scientist and have them be dead too, although that might raise too many suspicions straight away.

Anyway, if anyone has any thoughts/ideas/suggestions, please let me know.

Interesting problem you have there. I have run the scenario quite a few times now and have had to play with 3 a couple times but so far I haven't had too many players…

I do think the idea of having Helga be the next PC is a good idea however, with an odd number of characters I think it may be a bit tricky to make things extra for the Helga character. Since for each of the other player characters there exists a PC with goals that are basically opposite, you would need to come up with a way to do this with Helga as well, either with a PC or with an NPC at least. Perhaps Helga could be affiliated with (or possibly the boss of) the three smugglers. Helga was sent because the crime bosses thought that one or more of these three were not to be trusted and so Helga is undercover watching them. She would therefore have a vested interest in the other PCs not going to Cargo Module A (assuming she has regained that memory at the point they have tried to go in) and then trying to hide the fact that she is basically with the smugglers.

Perhaps not the most interesting back story but I think you could make it work.

Didn't see your message until it was too late. Anyway, I made her a drug addicted ex-olympic pentathlete (who was having withdrawl without realizing she was addicted), whose stash was in her dog's (who coincidentally has the same name as the Lunar slasher's original name) stasis carrier in the Cargo Bay that the other drug dealers aren't going to.
Worked well enough. They locked her and Theta in the cargo bay after she'd gone looking for her dog in there, they managed to get her out, then she recovered the memory about where her stash was and she managed to lie and convince them to let her back in there with it so she could go get her drugs.

Full write up in case it's useful to anyone.
https://docs.google.com/document/d/1FkyONQ29hCU-TkYz0M8WfiEZ2SvXFpCYAcn9QQR1vZg/edit?usp=sharing

Sorry I didn't see this question in time to answer. But I'm glad it worked out well enough. Thanks for sharing the Google doc!