Giving the appearance of a longer ramus. (photo)

Great question, and thank you for your picture.  Either fillers, fat grafting, or angle implants can help give the appearance to a longer ramus for your mandible.  However, if there  are issues with your occlusion (meaning, how your teeth come together), a better way of addressing this would be with orthognathic surgery.  Fillers are great in that they give you a "trial run" - get you an idea of what can be done.  Some people are happy with fillers - they can come and get things tweaked during their lunch hour with minimal downtime.  Fat grafting, while more permanent, is much more of a procedure and you need to see someone who specializes in fat grafting.  I suggest you consult with a few docs and see what options are available to you based on your mandibular anatomy.  Best of luck! I hope some of this helps.  

Yes unfortunately some people are just born with small mandibles.  If you want to change the way your jaw looks and feels, best to go with jaw implants.

Hi, the back portion of your jaw line is a bit weak and can be augmented, without making your face appear masculine, using precise placement of a dermal filler (I prefer using Restylane Lyft).  Fat is far less reliable at creating a consistent shape and volume than an off the shelf dermal filler or facial implant.  There are unwanted side effects with jaw implants and they could "easily" make your face appear very masculine which is not aesthetically beneficial for a female face.  I suspect that your chin may be weak.  This can be confirmed with non smiling photos of the front and side of your face.
Hope this helps.