Caveat: all of mine learn to go really well off of voice commands. I had a boss about 20 years ago that told me to talk to the horses all of the time. When you handle them, teach them walk, trot, whoa, back, turn, over (sideways), etc etc. Every time I interact with them in the field, the stall, or during an actual training session, I reinforce these verbal commands. As I teach them voice commands, I reinforce with body language/weight (usually my shoulder), or a hand placed somewhere (for back or over). When I longe, they walk/trot/canter, change (direction), easy (slow down), and cluck to go faster, kiss to canter or increase pace in the canter.
Now that they know voice and physical touch, they know that “over” and a hand on their side means move laterally. I teach sideways in the long lines by standing directly behind them, and as far away as I’m comfortable. I lightly flap one line against their side while saying “over.” As soon as you get even the slightest shift of weight the correct direction, stop the aid and give lots of praise. The more you do it, the more you can ask for actual steps sideways. This takes an incredible amount of patience, because some horses take multiple sessions to really get it. Never ever tell them “no” (they rarely know what that means anyway), just correct what they are doing. Are they walking forward? Use both hands to ask them to stop (I try not to say whoa because I do actually want them to move, just sideways). Are they backing up? Make sure the pressure on their mouth is zero and give a little cluck. They also might move into the line you’re flapping. You can switch lines so they’re doing the right thing and then praise them. Eventually they’ll get it, and give them all the praise!
Collection is a little harder, especially because she’s young and not very strong yet. Start by doing walk/halt/back transitions and see if you can see her lifting her back and engaging her core. Make sure she backs straight Once you can visually identify the muscles working properly, you can move into collection at the walk and trot. The biggest thing I worry about with the babies is them dropping their back and getting hollow. They have to learn to lift the back. When you ride, you can feel their back soften and come up or you can feel it drop and get tense. She’ll be able to have a collected walk for maybe 3-4 steps at a time in the beginning, and just 2-3 steps at the trot. The trot will look bouncy with more suspension (like in video 3 here when she’s doing it right. Don’t get greedy or she’ll fall out of it. You want to control the transitions. And remember, the more you do, the more sore (in a good way!) she’ll be the next two days.
For a 4yo I would work on “new” things maybe 10 minutes each time you long line, and broken up into 3-4 spurts. Hopefully you will be able to tell when she needs a break (trail swishing, getting antsy, head tossing, kicking out when she didn’t initially kick out, pulling on your hand, trying to walk off, etc) and try to stop before you get to that point. You want the sessions to be filled with her trying, you praising, and her continuing to try instead of her getting frustrated.