first ultra question (kinda long, sorry!)

Hello! I don't want to bore/annoy anyone, especially my 1st time on here; but I'm burning for a bit of advice.
I've been fantasizing about ultras for a couple of years now; I'm a long-time runner, love the marathon (between injuries); have been scared to break from my beloved routine, every time I'm out I tell myself that NOW is the time to switch to trails, stop striving to get back to the way things were before getting hurt, start fresh with no expectations, etc. but of course that goes out the window once I start running again. Recently "cam back" to NYC, surpassed my expectations (3:50:33, as an "old lady" of 55, I was quite happy).
Road running toward a spring marathon was going superbly, until I fell hard on ice Sat. Very bad (VERY lucky hip is not broken, merely "traumatized", pelvis is dislocated, chiropractic care is working miracles, but has hurl like hell :); we runners are toughies, though, right?); I'm out for the long haul. It might be weeks before I can even go out for a short easy WALK.
To my burning question :); is it reasonable to think I might be able to start preparing for a 50 miler (VT50) this Sept.? If I just start my walking/running on trails (there are some good ones around me, here in CT) and build up the way I do on the road?
Trying desperately to make good come out of this; this is exactly what I feared would happen in the woods! So I have no more excuses for sticking to what I know, or thought I knew.
Thanks for listening to me, I will certainly take any advice very seriously.

Elle - With your training base, you could easily train for a 50 in September. Most plans I've seen for a 50 are about 6 months long. I don't think you need to do all training on trails. In fact, if they are hilly trails (mountainous) you'll probably find they are too taxing to do continuously due to the pounding your body takes (downhill particularly). Of course if you can find flatter trails or dirt roads then the softer surface is in fact easier on the body than pavement. In my opinion, the key, along with total weekly miles, is to look at the terrain of the VT50 - elevation gain in particular, if it has a lot - and try to get some similar training in each week. Get a good ultramarathon book like Bryon Powell's "Relentless Forward Progress" to help you out with training and planning for an ultra. Hope that helps.