i can see where you are coming from, but as an outsider to your family i think the email was actually about the nicest one i can imagine from an anti-homebirth medical professional relative to a homebirth-planning first time mom. she does seem genuinely concerned about you and feels that she has information you may be unaware of which might change your perspective. i got the sense from the tone of the email that she would actually be receptive to some better studies of homebirth and an explanation of how you view the risks associated with home vs. risks associated with hospital. even if her background prevents her from being very open to suggestions that hospital policies cause women to die who would not have died at home, she would probably accept that there is a real risk to your newborn (and you) from the nastier bugs that run around in hospitals vs. at home. and she would probably take on board an explanation that homebirth in 2008 is NOT the same as homebirth in 1900 for many many reasons including advances in midwifery, hospital transport, nutrition, and screening out of high-risk mothers.
if you value your relationship with this woman (which it sounds like you should), i would try to tamp down my emotions and talk about it. you don't have to have one big talk, you can just casually respond to a few things as they come up. or write an email back, if you prefer. but if you do that, don't press send immediately, reread it a day or more later and try to make sure it sounds at least as respectful as hers did (and preferably more!)
you can try to address some of her anecdotal concerns. midwives have a lot of tricks for dealing with shoulder dystochia and as far as i understand it they are generally gentler and safer than vacuum extraction. i also think that midwives do carry forceps just in case. as for not being able to pee - my midwife inserted a catheter for me during labor (because i requested it, feeling that i had to pee but couldn't) and i barely felt it. properly trained midwives can do a whole LOT of what they would do in a hospital, is what i'm trying to say, and most people don't understand that. the only things they can't do are give you serious drugs (but they do have pitocin for possibly hemmorrage - why can i never spell that word??), perform surgery, or give you a blood transfusion.
as for the 14 yo dying of blood loss on the way to the hospital, i would say it's impossible to say much without more information. i know some midwives would consider a mother that young to be too risky for a homebirth, but i don't know if blood loss is a specific risk of being young.
anyway, i think you have a potentially great relationship ahead with this woman, really. she sounds reasonable and caring. my mil was not happy about the homebirth (although she was pretty quiet about it) until afterwards, but she came around and the issue has not been a problem in our relationship.