In reply to iusedtoclimb:
Am glad your wife is better. Obviously we don't know where you live but... it may not matter so much.
My guess (may be wrong!) is that your wife has lost a lot of confidence. If so, the physical may well be subordinate to the psychological, i.e. regaining confidence. I'd just start walking, on the flat, if need be. In fact the flat may be better, at least at first. Just get her used to walking, for half an hour or an hour, or whatever feels right for her. But keep doing it regularly (once a week, if possible), just so she gets used to walking again.
There are two ways she could go up Snowdon - pushing herself to the limit, a gruelling day out, or... just enjoying it, loving it. Getting to the second might be a longer process, but wouldn't it be worth it?
I'd start off small (really small!) and slowly, slowly build up.
Mick