We've seen this many, many times from new swingers. It is very common for a woman getting into swinging to find fault with her weight, appearance, etc. I can't tell you how many times I've seen this. Our society places enormous pressure on women for their looks, weight, clothes, etc. It's all bunk.
The swinging world is made up of people of all shapes and sizes. Your wife can't control whether people find her attractive or not. It's not up to her. All she can do is but her best foot forward. If another couple or guy doesn't find her attractive, so be it. On to the next.
As for swinging in general; now that you're talking about it, you need to have lots of conversations about it both in and OUTside of the bedroom. This is an important relationship step. Being turned on by it is pretty much a given (for most, anyway). Being ready to do it is quite another. Talk with your wife about this, about feelings, thoughts, situations, rules, needs, desires, etc. Rushing into it works for some couples but not most. This applies to her AND you. Being aroused by the fantasy of watching your wife have sex with another man is one thing; reality could be another. I find it intensely enjoyable, but some men don't react quite the same when presented with reality.