I just feel, with real friends, none of that should really be necessary, I can’t imagine going into such depths with any of my close friends, we would never try and take advantage of each other
This case aside, its not always about taking advantage it can be simple missmatches of expectations and missundersranding so its always best to just have that discussion.
E.g. you might be going to a foodie destination with a friend who likes to self cater cheap meals in to save money for other activities etc. Best work that out in advance.
Re "tipping off" the husband, the OP does not know why the friend has pushed her to cancel. Could be an affair, could be a simmering missunderstanding, could be that she just doesnt want to be friends any more.
To turn her husbands world upside down with no proof or evidence, not even a name! Is just nasty poing scoring because realistically, what can he do with that scant information?