It might all power up but it WILL have problems and will definitely need completely stripping, cleaning and likely need parts replaced. Anything made off MDF/chipboard will never be right because it’ll have soaked it up.
mechanical bits will never be right if they’ve been in flood water, I wouldn’t buy a tonearm that had been in flood water unless it really was cheap enough to throw away if it’s no good… you could send it to Audio Origami for a check over/refurb, but that not an inconsiderable expense… I’d just buy a properly clean example instead. Bearings, motors, switches are an unknown for long term reliability and because they turn, doesn’t mean they’re working right.
Switches/pots could be intermittent and could deteriorate too.
PCBs, actually there’s probably more hope for these than anything else, water, and particularly contaminated water can cause corrosion but the majority of corrosion seen on PCBs that have been wet is from where power has remained connected and you literally plate metal from components and traces positive rails to ground (or from ground to negative rails). If it was never powered at the time it was wet, I’d give a thorough clean with distilled water and isopropyl, preferably in an ultrasonic cleaner, but if not just a good bath and brush… then flush with more concentrated isopropyl and place in a location with some gentle airflow and heat. With this done you can check joints and reflow where necessary.
Does any of this sound like it’s something you’re up for? Do you think kit requiring this level of attention and still having the history behind it is worth even a fraction of the price of a clean non flood damaged example in its current state?
I picked 5%, because it does have a salvage value, but it’s not known what that value is exactly without delving in, and the time needed to delve in also has a value.
If it were me, I’d bow out, let your friend sort it herself and strongly encourage her to give full disclosure when advertising it herself.