Mom Needs to Go to a Nursing Home

Helping a loved one make a difficult decision when they are unable to care for themselves can be a very delicate task. No matter how careful you approach her, the outcome is not guaranteed. I do encourage you to work with her primary physician on this and be sure you have his support as well. He/she may also have some ideas on how to proceed since laws vary from state to state regarding diminished capacity for self-care. 

I'm not sure what you mean by an "intervention", but I'm going to assume that you are talking about having a family/neighbor meeting and have everyone tell your mom that she is no longer able to care for herself. You are right to be concerned about overwhelming her. For that reason, I think you should limit attendance to a few people who have the most influence on her, people she will or at least has listened to. 

Then, make the messages short and to the point, again to minimize the chance of overwhelming her. Expect an emotional response, and be prepared to provide appropriate support. Be gentle, warm but firm. I applaud you for being proactive, rather than waiting for something to happen first. I wish you and your mom and family the very best.