I thought perhaps that this delicately painted watercolor wreath of forget-me-nots and rose buds was sent to commemorate a loss, but I am not certain; it seems very possible it was made instead to celebrate an ongoing friendship, with the French "souvenir" simply signifying it as a momento; a literal forget-me-not! The valediction "devotre ami" seems more aligned with the latter possibility, simply meaning "from your friend."  I would take it now as a lovely token of friendships past, present and future, and a reminder to cherish and celebrate them. Certainly a nice gift for one of one's dear ones. 

6" x 3 5/8" and in very good condition, with a small piece of very old tape at upper left corner. Late 19th century or so I would think.