I'm so sorry to hear this happening to your wife, and on the left hand to add insult to injury! Frown

I suffered the same thing some 7 weeks ago. Lucky while unlucky, to my right hand middle finger. Wish I could say I was rock climbing/playing baseball/fighting a robber/saving the world, but I got my hand stuck in the sleeve of a sweater I was trying in a store, and somehow managed to break the tendon at the outermost joint. Probably couldn't repeat it if I tried...
Doctor's orders was a mallet splint for a minimum of 6 weeks, 24-7, and depending on the result, 2 more weeks by night. Since it's my bowing hand, playing has actually worked OK (had to lift the middle finger from the bow and use only the ring finger to stabilize the hold), could at least get through Mahler's 2nd with any serious problems. (I have also been able to do light training at the gym.)

I spoke extensively with a hand & foot specialist (who also crafted the splint out of wooden cotton buds and surgical tape!) about the prognosis, and she was adamant that if you take extensive care to never ever bend that joint during the healing (for instance, when changing the tape and cleaning the finger, which I did every 2 weeks) the finger should turn out fine. If the joint is bent at any time during that period, the healing process must start all over again.
So is there any chance at all that you wife accidentally bent the joint at any time? Even for a short moment? Also, it might suffice for her to just prolong the use of the splint. Unless there is some other issue, the tendon should heal if the joint is immobilized. Also, remember that healing can take longer as you get older.

I should add, that even if excellent care is taken during the healing process, upon releasing the finger from the splint, it will not be perfectly straight like it was before. I got out of the splint last week, (16 Apr) and my middle finger's tip is still slightly bent downwards. This may correct itself within the next 6-8 months. But you should be able to control the joint - although it will be quite stiff, sore and resistant during the first weeks!

So, I'd start by immediately stop bending the finger, and go back to using the splint for an additional 2-4 weeks (sucks, I know..!), and during that time trying to feel if she can make the joint "want to" move, inside the splint. After, if it still remains unhealed, it might very well be so that the injury must either be surgically fixed (as you automatically would if there is bone damage around the joint as well) or, the nightmare situation, it's chronic. In which case, I guess she would have to learn how play without the pinkie, which is difficult but not impossible.

I wish your wife the best of luck!