There can be little disagreement as to where the parts of this form begin and end, because the composer clearly lays them out, calling them couplets.
The A section, or the main theme, is a closed, 8-measure long period consisting of two symmetric phrases that are antecedent-consequent in nature because the first ends with an IAC in Bb and the second ends in a PAC.
The B section begins in m. 9, still in Bb majort. This theme lasts only four measures, ending on a HC in Bb in m. 12, which leads well into the return of the A section, which is repeated exactly as it was in the beginning.
The C section could be considered a B', because the melody in the right hand is the same as B for two measures (mm. 21-22). The harmony, however, is quite different - instead of staying on diatonic chords in Bb, Couperin modulates this section to minor - the relative minor. The A section returns again in m. 28 and again it is repeated as it was played in the beginning.
The D section could be considered a type of A' - the melody in the right hand is the same as the A theme for the first three measures of this theme (mm. 36-38). Once again, however, the harmony is different and Couperin modulates this section to F major, which is a closely related key. The A section returns again in m. 51 and is exactly the same as it has been in the entire piece.
Overall, this is a VERY straightforward seven-part rondo (ABACADA). The only unusual thing about this piece is Couperin's use of other thematic material in the C and D sections, giving this piece more organic continuity than would normally be found in such a strictly sectional piece.