Great job for your first test well done!!!! I LOVE the rhythm, you could set a metronome to it. Beautiful!
Biggest thing now for you is to start working on getting her to really push off from those hind legs so the forehand can begin to soften. LOTS of transitions, particularly trot-canter-trot, changes of rein (5 loop serpentines are great) and some leg yielding/shoulder in will all help you to engage those hind legs and get her softening over her back and through to the bridle. Also she is looking to the outside for the whole test. Teaching her should fore will really help with this ;)
In the test, RIDE YOUR CORNERS!! That's one of the biggest problems we have in Australia, people are lazy and just cut the corners, turning them into the edges of a circle. Corners are an excellent tool in a test, you want to use every corner you ride to rebalance and re-engage before the next movement. For say you have a medium trot across the diagonal. If you have a circle shape rather than ride the corner, you will struggle to get the 'check' back to set the horse up for the lengthening. Prior to a lengthening, I will ride forward into the corner, give a series of half halts and ride a very slight shoulder fore through the corner in really make sure I've got the horse set up for the lengthening. Once you've got a horse sitting on it's backside and up to the bridle, the lengthening will just happen of it's own accord ;)
So use your corners girl :) Ride right into them, half halt through them and DRIVE out of them. It will improve your test riding by miles ;)
Your trot-canter transitions need some work. She is running into them and then falling on the forehand when she finally gets into canter. It is all about the preparation and set up. Every stride you need to be thinking 'what can I change' 'what do I need to set up for the next movement'. I've been guilty of just riding the test as it is, a series of movements, without setting up for the next movement, I get to the corner and go 'oh shoot I have to lengthen and I havent prepared for it... oh well lets just wing it!'. Big no no,, you will never be an effective test rider unless you can prepare for each movement.
So for your canter transitions, in the test you rode in the video, I am assuming you had to ride a 1/2 20m trot circle then pick up canter at the marker am I right? If so, USE the circle. Half half half halt half halt! Check that you can move her, check that she's on your aids by asking her to come back ever so slightly them immediately forwards again. Re-balance her, get her back on her hind legs so that she can spring straight off into canter without this running flat out business. Check her with your outside rein, put your inside leg on and get a little bit of a shoulder fore feeling. She will most likely go straight into canter as she will be balanced ;) (can you tell I love shoulder fore as a preparation in tests? :P).
Throughout the canter, you looked like a good passenger. You MUST be the driver. So instead of just sitting on her hanging on and giving her a basic idea of where to go, DRIVE her where you want to go. Seat deep, keep half halting your outside rein to keep her back over those hind legs, and really ride her forward and up to the bridle. If you can get a balanced, controlled, calm canter in your test, the downward transition back to trot will be a million times better. Transitions are just so important in tests. Often the transition itself is worth double marks so you really want to get them right. A messed up transition can be take you from first place to 10th!
Another transition I want you to look at is the trot-walk. From trot, you are just pulling back going 'please stop' with no leg on. Downward transitions are actually very forward movements! You need some leg on to keep the hind legs activated and bring them under the horse through the stop so that they don't fall flat on the forehand. So a bit of leg, and check, release, check, release with your reins. When she is walking, don't pull the reins, put your leg on instead to keep the activity ;)
At the walk-trot, you want it to be much more active rather than having her just fall into trot. So work on getting her responding quicker to your legs when you're at home. A light aid with the leg and if she doesn't spring forward, give her a flick behind you leg.
Second canter transition was much better
I like the free walk, she has lovely big hind leg steps there. Only thing I'd like to see is a little more stretch from the wither with a slightly rounder neck in the free walk, but that will come as she learns to travel more efficiently overall.
Down the centre line, ride with a purpose. Don't think of it as 'oh finally it's over I'll be out of here in a second!". Think of it as the final impression you give the judges. If you finish by dawdling down the centre line and a sloppy halt, the judges will remember you with that, it will be the last movement in their mind and as they are writing up your collective scores they will always have the sloppy image in mind.
If you ride down the centre line with a purpose, a big smile and get her really active, marching down the centre line like you own the place, an beautiful crisp square halt and a big smile at the end. THAT is what the judge will remember and it will likely show up in your results in the collectives.
Overall, she's a very nice little mare, 3 nice paces (love her walk!) and could really do quite well once she learns to use herself in a more effective manner. Keep working on it, you're doing brilliantly *thumbs up*