If a guy wanted to send a girl some flowers in appreciation of a great time.  What would be the best way to do it? Independent or agency...

A gift on money is usually appreciated best. Tip her well at the end of the appointment if you had a GREAT time. Keep in mind that a lot of the girls have SOs,BFs or others in their life and sending something to her may place her in an uncomfortable spot. Make sure it is OK to send something (if that is the direction you are headed) although I can't believe that many girls would give up a home address for safety reasons.

Call the florist and make the order and tell the florist that the lady will call in and give directions whether to deliver and, if so, where, or when she will pick them up.  Choose a florist in the area of the lady's incall for convenience.  It doesn't matter to the florist what name is given, so long as the order and the lady use the same name.  No ID check should occur.

some ladies are allergic, but the green of cash is always welcomed

I think that is great that you tip well...I've been around for sometime now and have great reviews. I know that I've had many great times, but have never been tipped....not that I'm complaining.