Her doctrine clearly contradicts that of the anarcho-capitalists who see no role for government in the function of the markets. This is not a minor difference, or a difference only in degree. This is fundamental.
Rand believes in absolutely minimalist government, anarcho-capitalists in no government at all.
Let’s assume a scale of government control of society and the economy from 0 to 100, with Stalinism at 100.
On that scale Rand would be a 1 and the anarcho-capitalists a 0. To my mind that means she has a whole lot more in common with them than with anyone higher up the scale. But I guess that depends on how you define “fundamental difference.”