I think, before you decide what you can and can't do, you need to find out a bit more carefully what this lady is actually wanting. A lot of clients, particularly brides, book in for manicure & pedicure, but when asked what they want to actually acheive, they are really more intersted in the end resut of their fingers and toes polished/enhanced and looking good in preparation for the big day as opposed to a pampering relaxing manicure or pedicure!
I wouldn't offer full spa manicure or pedicure before a spray tan...as it involves 'oaking the hands or feet, and it does affect the outcome of the tan, as doe sthe creams that are applied, but I frequently do express mani/pedi (ie cuticle tidy up, base, polsh top coat) or gel fingers and toes with a spray tan, with great results, and some very happy customers.