At 51, if the main concern is sagging in the lower face, jowls, jawline, and neck, the most effective option is usually a lower face and neck lift. Non-surgical treatments can improve skin quality slightly, but they usually cannot lift true tissue descent or redefine the neck in a lasting way. From your photos and description, filler alone would likely not be the best solution. Filler can soften hollows or folds, but if too much is placed in a thin face, it may create heaviness or an unnatural look rather than correcting the sagging. A good facelift should address the deeper support layer, not just pull the skin. Depending on your anatomy, this may involve a SMAS or deep plane technique, combined with neck work such as platysmaplasty, conservative fat contouring, and skin redraping. Because you are petite and low body weight, volume loss may also be contributing to the aged appearance. In that case, small-volume fat grafting or very conservative filler can be useful as an addition, but it should not replace lifting if the tissues have descended. My advice would be to consult a facial plastic surgeon or plastic surgeon who performs many lower face and neck lifts. Ask whether your main issue is skin laxity, jowling, platysma, fat, or volume loss. The best result will usually come from a customized lower face and neck lift, with subtle volume restoration only if needed.