One factor that your question depends upon is whether women are obligated to daven Mincha. The Rambam[1] says that women are obligated by Torah law to daven daily. However, the Torah law is fulfilled by any request made during the day, and the rabbinic decree that one daven set prayers twice or three times a day[2] is time-based. Women, who are not obligated in time-bound commandments, may therefore not be obligated in the formal structure of Shacharit and Mincha. Many women follow this approach and suffice with a short prayer/request daily.[3]
In contrast to the view of the Rambam, the Ramban[4] maintains that tefilla is entirely a rabbinic obligation. Because of its importance as a means of requesting mercy from HaShem, the Rabbis obligated women as well. Accordingly, women are obligated in at least the essentials of Shacharit and Mincha, just like men. The Mishna Berura[5] prefers the Ramban’s opinion.
One major difference between the obligations of men and women concerns Ma’ariv, which is essentially a voluntary tefilla.[6] While men accepted it upon themselves as an obligation, women did not.[7] Another difference is that women who are especially busy, in particular those responsible for the unpredictable needs of small children, may be exempt from Shacharit and Mincha, either by relying on the lenient opinion of making a short prayer/request or because their involvement with the children exempts them.[8]
You categorize yourself as one who davens Shacharit and Mincha but not Ma’ariv, and thus your situation is as follows. If you are obligated in Mincha to the same degree as a man, you should daven tashlumin (a make-up prayer) for your missed Mincha, just as a man would. However, tashlumin was instituted to be recited after the next established tefilla (in your case, Ma’ariv). In fact, if one does something that shows that the first tefilla he recited was the make-up, preceding the set tefilla, he does not fulfill tashlumin.[9] Thus, if you do not daven Ma’ariv, you will not be able to daven tashlumin; you cannot wait until Shacharit, as tashlumin must be done at the next tefilla period.[10] (One could raise the argument that for a woman, Shacharit is the next tefilla after Mincha, but Rav S.Z. Auerbach rejects that logic.) Even if you are not obligated in Ma’ariv, if you choose to daven it, you can then do tashlumin.[11] However, it is unclear whether you are required to go so far as to daven Ma’ariv in order to make tashlumin possible.[12]
A claim might be advanced that one Shemoneh Esrei at the time of Ma’ariv is sufficient, as a woman is obligated in one tefilla other than Shacharit. Usually, the second tefilla is Mincha, but if a woman davens Ma’ariv voluntarily, she has recited the correct number of tefillot. However, this reasoning is flawed because she was supposed to daven Mincha, and when she missed it, she is expected to daven tashlumin. A normal Ma’ariv fulfills neither Mincha nor its tashlumin. In fact, if you were to daven Ma’ariv, you would be required to daven the tashlumin for Mincha.[13] Thus, while it is questionable whether you have to daven Ma’ariv, if you do so, you will have the opportunity, and thus the obligation, to say an additional Shemoneh Esrei at that time as tashlumin.
If a woman has not accepted upon herself the obligation to daven Mincha, she obviously cannot be obligated more in tashlumin than she is in the original tefilla. There may be an issue if a woman tries to daven Mincha fairly regularly except when she is quite busy, but on a given day she forgot without a real excuse. However, even in that case, she is presumably not obligated in tashlumin, since she does not treat Mincha as a full obligation.
In summary, in your case, it is unclear whether you must daven Ma’ariv, but if you did, you would say two Shemoneh Esreis. While it is difficult to mandate davening Ma’ariv under those circumstances, we suggest that it may be worthwhile,[14] especially if it makes you feel better or will help you remember to daven Mincha in the future.