I’d go with co-worker, someone who has an interest with you being “out of the way” for her to get a promotion she wanted. But someone you thought is a good friend before shrinking.
Definitely an interesting concept, I used to work with a woman that I thought was a really good friend turns out she isn't friends with anyone male or female that leaves the company and likes to use them while they are there, she'd make someones tiny life a nightmare.
I’d go with co-worker, someone who has an interest with you being “out of the way” for her to get a promotion she wanted. But someone you thought is a good friend before shrinking.