Greetings. This is a great discussion and thanks for initiating it!
My very first thought after reading the original post was "she would not be a candidate for a homebirth", with all the complicating factors that you listed, I personally would not feel comfortable with out of hospiatal birth for this Mama. All the listed conditions, especially added up together, make this Mama high risk and greatly increase her risk for PPH. (Her gravidity status, by the way, does not bother me, and that alone would not cause me to "risk" her out)
All that being said, the worst PPH I have managed (2500cc) happened in a 100% normal, low risk healthy, primiparous Mama in an out of hospital setting. In my practice, we work with herbs, homeopathics and alternative modalities very frequently. However, in the face of signifigant hemmorhage, I will not hesitate to use pharmeceuticals as my first line. In my particular situation, the Mama had had a completely normal course of labor followed by a beautiful physiological second stage and birthed a healthy baby girl. At approx 20 min PP, before the birth of the placenta and with an actively latched and suckling baby, it was as if a hose was turned on. My assistants and I did several things at once...I completed a manual removal of her placenta, oxytocics were administered, an IV was started, O2 applied and a urinary catheter was placed. Despite all these interventions the bleeding continued and I preformed bi-manual compression...all the way to the hospital, in the ambualnce...we were transferred to the gurney together. Thankfully, she recovered well and quickly. Those of us who attend birth, must be prepared to intervene quickly and approriately on the rare occasion it is warranted. One of my collegues explains it to families as, "I know a lot of things and tricks, the best births are when I do not need to use them!" As guradians of birth, we must be just that, guardians and always watching with a critical eye.
On the subject of oxytocics before the birth of the placenta; the argument that they will "clamp down the cervix" has been around for a long time. It has never been documented or "proven" in the literature or research. After the birth of the babe, the cervix will close up somewhat on its own, as there is no longer a fetal head pushing down on it....
Again, great discussion and I can't wait to read more insights!