The relationship between menses and DCS is complex, but in part, related to the presence of any underlying anemia, edema, hydration state etc. What this means is that gas dynamics are altered : both uptake and offloading. Uptake because in the presence of any anemia the cardiovascular system is under greater stress to achieve the same amount of work, and offloading, because there are changes in the tissues. How much is unclear. Add to this the potential presence of oral contraceptives,where there is the additional change in the tendency of the blood to clot, and both gas and blood vessel dynamics are changed.
As noted, there has been a "tendency" for women who are menstruating to have a slightly increased risk, but this has never been verified, and is in the realm of physiologic reasonability.
As regards, the risk of toxic shock, there is no "free flowing connection" between the tampon and the exterior, and the normal precautions should be taken.
Overall, I would suggest that a woman diver be somewhat more conservative during this time. After all, DCS risk is based on mathematical models of our interpretation and understanding of normal physiological behaviour. Each of us function as physiologically unique to some extent. This has been demonstrated by the development of DCS by a diver who has repeated the same exact profile. So clearly there are unknown factors at play which we can hope to pre empt and act accordingly.
I'm not sure if that helps, but hope so.
Safe diving.