Well you are without doubt right that Gaius is too late for EB, although he is widely used in studying what Roman Law was because his work is closest to it's original form. Your english is top of the line compared to many English to, I actually thought you were a native speaker at first.

Gaius is a good source, but the translations I have read, and done myself of him doesn't support you. Here is a good translation of him, the institutes could be found at the Latin Library if you have a different translation. I personally would also point to David Johnston's Roman Law in context, since the translation of Tutor as Guardian isn't accepted by everyone. Anyway I believe this is the section you are reffering to if you are reffering to the Institutes of Gaius.

(190) There does not seem to be any good reason, however, why women of full age should be under guardianship, for the common opinion that because of their levity of disposition they are easily deceived, and it is only just that they should be subject to the authority of guardians, seems to be more specious than true; for women of full age transact their own affairs, but in certain cases, as a mere form, the guardian interposes his authority, and he is often compelled to give it by the Prætor, though he may be unwilling to do so.

(191) Therefore, a woman has no right of action under the guardianship against her guardian, but where guardians transact the business of their male and female wards, they must render an account of their guardianship in court, after their wards arrive at the age of puberty.
My point is also that she could, even on alienating Res Mancipi according to Julian the case of land being sold by women would be settled as sold provided the buyer paid for it, Julian was early 2nd century ad though, so questionable if he applies to our time period.

My point is women were able to conduct business and own property for themselves, and it wouldn't be uncommon for their husbands to be off at work in the provinces or on politics and for women to run the estate.