My busty Indian wife for gangbang

Has she been with another man? Usually, unless the circumstances are unusual, its a progression - one man, two men, many men. Usually, you need to help her build confidence, feel secure, protected, and safe to do a gang-bang.

Certainly there are exceptions, but we lack context to offer better advice. Sometimes sharing feedback about the comments on her photos can be a motivator. Have her imagine the possibility of hundreds of horny men, jerking, stroking and cumming, looking at her photos, imagining her pulling a train, or as the center in a gonzo, dog-pile style gang-bang.
That’s how it went with my wife - first one man, then she wanted 2, and so one. The most she has done is 6, which to me qualifies as a train.
 
Seems that - even when she cheated - she fucked only one guy at a time. Rather than going straight to a gangbang, have you considered starting with a 3some? If she agrees and gets into it, she might then consider adding more guys. She certainly has the body to handle multiple cocks!
 
I talked to her regarding threesome, but she got angry at that moment. Later when we were having sex, she kept asking me about threesome. It's confusing for me to understand her feelings for threesome or gangbang
She is probably confused by her own feelings. Women often have a mix of feelings about such things - guilt, fear, lust... I'm sure there is a part of her that feels guilty about the past and perhaps causes increased feelings of guilt about doing anything again. Then fear that maybe its a trap or you'll change your mind or become angry after it happens. Often a thought that having her get with another man is an excuse for you to go be with another woman. Then during sex, we all are under the greater influence of lust, which makes us more open to things, even if they are just on a fantasy level. She may want to just fantasize about it for a while during sex and may perhaps progress from there or may just want to keep it a fantasy but, either way, there is some opportunity to have fun with the idea.
 
I talked to her regarding threesome, but she got angry at that moment. Later when we were having sex, she kept asking me about threesome. It's confusing for me to understand her feelings for threesome or gangbang
While having sex is a great rime to discuss her having 3 some and then a 4 some and moresome, tread lightly and listen to her responses.