Well a level of 55 means that she is definitely pregnant! It doesn't matter what the level is at but it needs to double every 72 hours (3 days). She needs to get it checked again to see that it goes up.
There really isn't a way to prevent miscarriage (what we call abortion in the USA) unless your wife has a fertility problem. If she miscarries again, further tests need to be taken to see WHY she is miscarrying.
A few things to consider:
1). Did they test her progesterone? It should be above 15 and if it isn't, they should supplement her with progesterone.
2). Is she taking a baby aspirin? If she has an undiagnosed blood clotting disorder (which can cause miscarriage) this would be beneficial.
3). You should wait 1-3 periods before conceiving after a miscarriage. Like I said before, getting pregnant right away won't cause or prevent miscarriage. They usually happen for reasons beyond control.
Good luck and congrats! I hope this little one makes it and you guys are blessed!
I have to add that I have had 2 miscarriages. I also have 2 beautiful daughters. Normal pregnancies with them. So it is possible that this little one will be just fine. Good luck!