Complex sentence: Eritha probably asserted her claim on behalf of the goddess Potnia, thus that the land of the sanctuary should be classified as a privileged one, presumably free of obligations, rather than a regular leasehold which would have been subject to taxes.
Split into simpler sentences: Eritha probably asserted her claim on behalf of the goddess Potnia. Thus, according to her, the land of the sanctuary should have been classified as a privileged one, presumably free of obligations, rather than a regular leasehold subject to taxes.