Adding my fiance as an Authorized Payer to help her credit score.

I'll try to keep this to just the important details - let me know if I've left anything out.

My finance and I have been looking at buying a house, but her credit score was not good... mid 400's (long story how it go there). Over the past 5-6 months she has brought it up to 578 by paying off all of her debts, opening a secured CC, etc.. Most of that increase happened in the first couple of months when she really took on the task of repairing her credit score. Recently it seems like the increase has gotten a lot slower though.. only jumping 15 or so points in the last couple of months and we are wondering if adding her as an authorized payer to my Bank of America CC would help to boost her score.

Right now I have a pretty good credit score (741) with a credit limit of 12.5K on my BOA CC with a standing balance of 5K - so about 40% utilization rate. I pay a little over the minimum payment on time every month and have had the card for around 8 years and have been really good about making payments on time (I think I was late a couple times early on but have been really good about it since). I know it's not ideal to have a running balance like that and getting my CC debt paid off is our next goal once her credit is fixed, but for now we are wondering if adding her to my card as an authorized payer would help her, and if so, how much? I hardly ever use my CC anymore and the current debt was obtained early on when I was in college - so I don't anticipate the utilization to increase.. not sure if that matters or not.

Any input is very much appreciated