If there is not currently a site on your clients domain, that's probably the reason it was declined. I'm assuming that is the case since you said the site was ready to go live - not that it was live.
I know that Paypal will not upgrade to a Paypal Pro account unless there is something there for them to look at. If all that's there is a coming soon or a under construction page - Paypal will always decline.
She also needs to have a verified Business account with them - a checking account debit card is really all she needs for that - not an actual credit card.