I don't know what missionary work is like, but my family travels to Panama regularly and they have nice things to say about Panama City. She could do worse.
My (non-Mormon) experience over several visits to Panama a few years ago was quite positive.
Surprisingly so, so I asked around. I'm a U.S. citizen. Many Panamanians have positive feelings toward Americans because of the return of the Panama Canal, which has resulted in billions of dollars injected into their economy.
An example: with a group of friends from Costa Rica, Panama, and Colombia, I went to visit a mutual acquaintance in a high-security prison deep in the jungle. Whereas my friends all had to go through serious security, including strip searches, entering the prison, I was waved through without even going through a metal detector. Then, just as we entered, it started to pour--a real jungle downpour. The warden immediately sent a trustee with an umbrella to hold over ME so I wouldn't get wet--even though he didn't now me from jack.
Not sure if the missionaries will get similar treatment, but it sure didn't hurt that I had a U.S. passport.
According to Cumorah.com the Church in Panama has 71 units down from a high of 112. It grew under 2% last year increasing by 800 people. The activity rate is about 11% , so she may spend alot of time doing reactivation! Evangelicals are about 40% of the population with SDAs and Jehovahs Witnesses both much bigger in active members and numbers of congregations! Good luck!