Do I have Any Right to be Upset - Also Need to Vent

I think that due to her tiredness your wife can't handle to deal right now with the hard part of her friends character and their relationship dynamic. After a good rest you can talk to her about it in a calm manner and see what she has to say. Some people are bossy and needy but there is always a reason they remain a friend. Probably the "friend" gives something back in return and that's why your wife chooses to help her out. Might not be the same sort of help but something different. But I think that yes, you are right about one thing. I can understand that we sometimes step back for our friends and give them what they need without questioning. But if this becomes a habit it is unhealthy for a relationship, except if both are truly happy with this outcome which I sincerely doubt.
Btw, did I get that right? You had a panda in your home or was that a figure of speech?

One thing I've found. When the wife is angry, I listen and agree with what she says. Giving advice when it isn't asked for is just too dangerous.

To step into the conflict without being asked could make your wife feel like you don't think she's strong enough to handle it.

There are different dynamics to each relationship, and I can only speak from my own experiences.

I agree with Arcadeus! Between my friends issues and mine I would never let my other half step in for me. However! Stepping in on an issue and getting in the middle is different from simply having a conversation with my other half. I wouldn't want him to bottle up his feelings for jack-squat. To me that's saying that I can't handle how he feels, and let's face it if you can't tell your partner how you feel then there's a problem. I think she would be more offended if you bottled up than anything else.

That aside, when you do bring this up and you should because it's troubling and she's your wife. A calm environment is good also bring up this as a trust issue because that's what it is. Your wife's friend can't trust her to take care of the trash panda ergo M must nag and badger. Put this way it makes one take a step back.

It's always good, in this kind of a situation, to decide what YOU want to do. You can't change anybody else. If your wife is being manipulated but refuses to see it or admit to it, there's nothing you can do to change that.

The only person you can change is yourself. Basically you can't control what other people do, but you CAN control what you do about it.

For example, you can tell your wife that whatever she gets herself into via M, raccoon, whatever, that you want no part of it. You don't want to hear about it or get embroiled in it. You don't want to look after the critter, or any other critter.

Your wife is entitled to her friends, whoever they are. What she doesn't have the right to do is dump her friend's problems or concerns on you. Make it clear that she will need to deal with this herself.

Just say that from now on, you don't want a part of this debacle—nor be offering any sympathy if things go bad. It's up to your wife to shoulder responsibility for this mess.

Yeah. You don't have to fight about this or create WW3. Just stay calm and tell her what you are going to do. And stick to it. Let her work around YOU. It's a technique that works, because it doesn't force the other person to change, or turn into a nagging match or a fight. You just say something like "I'm not comfortable dealing with this issue any more, so I'm going to ...." whatever you're going to do. Let her know what to expect from you, and then make sure it happens.