To be honest, I think it's clear that Mary's intentions isn't to harm the new players and steal from them etc but I don't think that her intentions are completely innocent either.
What I expect to happen is that these new players which passes through Mary's town are eventually going to leave one by one to start something of their own or join a more established town that isn't just a bunch of plots and a few shared resources sections.
Mary will eventually attempt to manipulate these players into letting her into towns they may have gotten into etc. I don't think that Mary is capable of doing ANYTHING for ANYONE without some kind of benefit from it but that's just my 2 cents.
If this does happen, good luck to the poor souls, I'll just sit back and laugh because it won't be happening to me
EDIT: I don't think that Mary's town will protect any of you newbies from attackers.