First, did you wife put on any sunblock? Did she wear long sleeves or using an umbrella or wearing a hat to avoid the sun exposure? If not, she needs to start using it. I now reside in Hong Kong and the sun is strong too, and I am advised by my rhumty that I have to put on sunblock whenever I am out.
Second, if you are thinking about the North America or even Europe, like UK, you have to also consider the cold weather which will affect the toes and the fingers (Raynaud's phenomeon), and your wife must be kept warm when outdoor.
I had lived in Canada, United States, and United kingdom before. I think my condition is better when I was back from Canada because the rhumty treatment in Hong Kong is more aggressive than it was in Canada. In Hong Kong, the rhumty is willing to give me Prednisole, while the rhumty in Canada did not (but I am talking about more than 20 years ago).
When I went to the US, I think my SLE gets better. There is no actual prove, but I do think that weather contribute a lot. In Hong Kong, the humidity is high and it could affect the joints. In the US, it's drier, and it helped a lot.
I think, however, another important factor is the use of medication. I started using Cellcept in the US and continue using it in UK and in Hong Kong, and up to this moment, I do not have any flare. Mind you, I am using sunblock when I go out, and try my best to avoid too much sun exposure.
I hope these help.