The ornamental design for a collar for a babybottle, as shown and described.
FIG. 1 is a top perspective view of a collar for a baby bottle, in condition of use;
FIG. 2 is another top perspective view of the collar for a baby bottle of FIG. 1;
FIG. 3 is a front view thereof, enlarged for clarity of disclosure;
FIG. 4 is a back view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a right side view thereof;
FIG. 7 is a top plan view thereof; and,
FIG. 8 is a bottom plan view thereof.
In FIG. 1, the broken lines showing a nipple and bottle depict environmental subject matter and form no part of the claimed design. In FIGS. 2 and 8, the broken lines depict portions of the collar for a baby bottle that form no part of the claimed design.