You need to (gently) help her to see how the JWs have been completely deceptive when it comes to showing survival rates and problems associated with insisting on bloodless options. Have a look at Gladring's recent post to see how they are still misrepresenting this even in a very recent Awake! in the Watching the World.
If everything was how those videos/dvd made it seem, then why would anyone accept blood? Makes no sense. So prepare a little info that you can show your wife. Its easy enough to find that stuff online.
Letting go of the blood issue was a BIG deal for me as I was convinced bloodless was the best way to go (excuse the pun!) but now I'm prepared to do whatever needs doing to save a life, my own or someone elses. Life is too precious to do anything less.
The people your wife is studying with have probably already warned her to expect persecution and so that's likely how she views it when you say anything anti-witness. That's why I'm saying to you to procede gently and not get her defenses up.
PS Look out for a PM