There will be a balance for 36 months, why would it only lower her score temporarily? Is there also a concern of credit being to high as it relates to income? I will likely need to lease/finance my own vehicle in next year. Combined we have some 60-75k >>available<< credit on CC's (pay in full monthly). Show income of approx 115k.
Temporarily I mean as long the lease is in effect.
You have to see how much available credit your wife has. And how much the lease/loan will be and if it's more then 10-30% it will definitely affect the score again only temporarily until the lease is paid up.
If your going to take out a lease yourself as well, take that into consideration that you might be paying more for the lease since the score might be lower then usual because of the lease that's already on the credit report affecting the utilization.