Never a line of three just two because that's where her confidence was. She can jump a full 2'3 course.. just 3 jumps in a line so close was past her comfort zone.
This is backwards thinking. "Three jumps in a line" or gymnastics or grids are MUCH easier for the horse than a single fence. When a gymnastic is set correctly the horse doesn't have to adjust stride or see a distance; the way the exercise is designed sets them up for success and builds confidence.
Conventional training involves lots of simple gymnastics and grids at low heights to teach the horse first, how and where to "wear" their fences safely, and later, to adjust their stride to jump from a difficult of wrong spot. Single fences and courses come much later as their flat work progreses as well.
The normal progresion of training is cavaletti (poles on the ground only), then cavaletti followed by a single fence, cavaletti followed by a simple gymnastic, then more complex gymnastics, then single fences with placement rails to assist the horse, then lines and other related distances, then simple courses all kept fairly low as the horse builds confidence. The horse should also be jumping higher in a gymnastic or something with a fail safe distance than she is a single fence or course. Somewhere between single fences and courses you do a lot of work developing pace, three clear speeds at the canter, and adjusting pace and balance between fences before attempting courses.
Jumping a full 2'3" course and a single fence of 3'3" on a horse that can't confidently negotiate the little gymnastic in the video is backwards and a little scary.
She's always been one to jump long rather then get to close to it.
Because you haven't *taught* her where to jump from to do it safely and correctly, her jumping from "downtown" is a result of inexperience and possibly a little fear.
She is a lovely horse with a good attitude and some real jumping ability.
There are lots of good books and resources out there on starting a young horse over fences, do yourself and your nice horse a favor and do some research. Figure out a safe, logical progression of training for her rather than just randomly pointing her at stuff and hoping she figures it out.