Tam would actually deconstruct the magnets. By doing some clever tricks with lasers she can actually vaporize the magnets and distill them into their chemical and atomic components. There are a lot of useful elements and compounds that can be found only in magnets, especially if you are making more carefully manufactured magnets. Of course in a long ocean voyage Kay and Tam would have discussed all of this, but illustrating those discussions would have been beyond boring, so I have them wandering around the streets of Sausalito while having this talk.

My proofreading team (ok, my kids) asked why, if Tam can make water perfectly invisible, does she not look solid? The reason is not because she has to be transparent, but because if she was perfectly realistic to Kay then he might forget that she wasn’t really there. At least if someone catches him talking to her, he can claim “It’s a new Bluetooth set of eyeglasses! Cool isn’t it?”, but if he starts holding doors open for invisible people he would start to stick out. It could even lead to accidents. Better if there is a constant reminder that she isn’t really there.

↓ Transcript
Scene is on the city streets of Sausalito.
Kay: ... so the programming is fine, but you have to take a trading loss occasionally, or you'll be noticed.
Tam: Agreed. I will switch 90% of the trades to be completely random.
Tam and Kay come to a Hardware store (Waterstreet Hardware & Marine)
Kay: This store?
Tam: Yes, let me show you the list.
A rectangle appears in front of Kay.
Kay: Three pounds of magnets? What are you going to do with three pounds of magnets?
Tam: I have plans for a fusion reactor.