With any Her2+ breast cancer, herceptin is recommended as it is highly aggressive, even in stage 1 and small tumors (less than 1 cm.) There have been a couple of studies that have found the recurrence rate (even when tumor is small) can be as high as 23% when chemo and herceptin is not given. With chemo alone, I think the recurrence rate was about 12-13% Herceptin use cuts that down even more to about 7%. Herceptin is very expensive, though (about $10000 monthly) but in most areas, it has become considered the "standard" of care for Her2+ regardless of size.
Herceptin is the right choice for HER2+ cancers. It's used widely in the US with great results. As Bluebutterfly said, she has an aggressive cancer even though it was found at stage1. That was lucky for her. She runs a much higher risk of recurrence or another primary tumor.
Keep researching and best wishes for your wife during her treatments.
You should address your questions and concerns to your wife's oncologist, who would have all the test results and information specific to her case.
However, HER2+ tumors are considered very aggressive and herception is a targeted treatment for them. It would be highly recommended, if you can possibly find a way to afford it.
Best wishes...