It seemed to me like Camille did think the two would connect, and to me, it seemed a bit tone-deaf for her to have deliberately placed her friend in such a questionable situation. If Pru needed male companionship, Camille should have let her find it on her own. It seems like Camille was always there for Pru as a friend, so it's not like Pru had no one to talk to.
I've got mixed feelings about this scenario. On the one hand, life's too short to be unhappy if one has control over the situation. On the other, one is obligated to one's marriage vows. However, since Spence really wasn't "there" anymore, and since intimacy with someone outside the marriage seems preferable to divorcing Spence so she could move on with her life, I tend to feel like connecting with Walter was an OK decision, and wasn't unethical. Definitely a gray area, though!
I DO question the fact that she chose Walter, though. I thought he was kind of demanding and an "always right" kind of person; a bit of a jerk. Plus, he's the first male she started getting to know after Spence's decline began, and I'd think she'd be better off shopping around more.
I also question the fact that she lied to Ginny about her whereabouts. That says to me that she, at least, felt she was behaving in a less than honorable way.