Rather than having HIV/STD testing before every new sexual partnership, it would make more sense to just plan on visiting a GUM clinic about once a year or for chlamydia, gonorrhea, syphilis and HIV
testing. Obviously, you also would do so if you develop symptoms
like discharge from the penis or penile sores, and perhaps if you learn that a partner was at particular high risk. However, your prospective new partner doesn't sound especially risky to me, even given her South America adventures.