Those figures look about right, I think the missing factor is that of 'effective dose', ie the whole-body dose associated with the same overall risk. When only a small part of the body is irradiated, such as the breast alone, a tissue weighting factor is applied to calculate the effective (whole body) dose with the same associated risk. Some organs and types of tissue are considered more sensitive to radiation and have higher tissue weighting factors than others. For breasts the factor is 0.05, which if multiplied by the 0.7 mSv mentioned above gives 0.035 mSv effective dose - not far off the figure for the long-haul flight, for which the whole body is exposed of course (tinfoil hat or no tinfoil hat....)
So in a way, she is probably correct as long as she has a whizz-bang newer digital mammography set to use rather than the old style which would I reckon give more than 0.7 mSv.
