Currently enrolled in the MSc Economic History at the LSE, so I figured I'd chime in. As far as I know it's the only university with a stand-alone economic history department, and now offers postgraduate options in both "Economic History" and "Quantitative Economic History". The former is fairly flexible in terms of the course options you have, while the latter is built around the standard postgraduate economics core. Your friend could study both topics within the department (there's a pretty wide range of faculty, honestly), but, as chateauheart and tm_member pointed out, the necessary skill sets don't overlap all that well. Oxbridge has some programs as well, but I believe they are in "Social and Economic History" so you're looking at a slightly different environment.
For the US, things are a bit trickier. Before applying, they'll really need to decide if their primary methodology will be economics or history, as both departments often have people doing related research. In terms of economics departments (adding to the earlier list), I know Yale does quite a bit on EH and I think Vanderbilt has it as a field option. I don't know anything about the program at Maryland, but they seem to offer a "Trade, Institutions, History, and Political Economy" field. In terms of history departments, there will be a scattering of folks at a good number of universities, but where they apply would depend much more heavily on the specific type/country/era of economic history in which your friend is interested. Temin has a working paper from 2013 on "The Rise and Fall of Economic History at MIT" that gives a good feel for the situation in the US.
Overall rankings can be a bit difficult to make because, depending on how far they shift to the historical side, that can almost involve a completely different job market.