I made my first wedding cake, (the hot pink scrolls in my photos) and the customer requested the top tier be plain white, they were going to add ribbon around the top tier, and flowers as a topper on site. The cake IMO just doesnt look "finished" enough to advertise it AS a wedding cake. Should I ask the customer if she could send me a pic of the finished cake?

Yes.
Tell you would love to see it with the topper added.

I do it on every wedding cake I do. This is how I handle it.
After delivery (I take my own pics at delivery for security purposes and try to get great pics there) I come home and email the bride and say
"Just wanted to thank you for your business. I hope that your wedding day has been all that you imagined. If you dont mind, I would love to have a professional pic from your photographer of your cake and would love to see how beautiful you looked in your gown.
yada yada yada.
You know....something along those lines. I have been successful in getting great pics of my cakes. It really helps your portfolio look good. Take a look at my site (www.couturecakecreations.com) to see what I mean.

A number of my brides email me pics of the cakes. On the few times that I've forgotten the camera, I ask them for the name of their photographer so I can order a pic.....they usually just email me one.

A marketing guy told me that you should have pics of people enjoying your product. So a pic of the couple cutting your cake is better than a pic of just your cake. (ever see a hot tub brochure with an empty hot tub? Nope! You ALWAYS see people having a party in one!). Plus brides luv sending their friends to your website so they can say, "Look! Look! Debi put us on her website!"