As per FIG, you can mount either side, just you can't move the reception (dismount) mat.
However, in small/local meets sometimes you are limited by the space in the venue and sometimes you might only be able to mount from one side or end of the beam.
Probably, if it is not affecting the technique or the future progression of the skill and is a minor and not easily fixable thing (without maybe messing with other potential problems), they prefer to focus on other corrections.
I'm thinking, from what you said, she's probably arching to pass over, instead of leading with the toes. So I'd work on doing giants to like 45 degrees, focusing on scooping and leading with the feet.
For at home probably back extension rolls focusing on staying hollow.
Press handstands are a good indicator of a good flexibility-strength-body weight ratio. Which usually correlates with good physical qualities for gymnastics. But it is not absolute and there have been good successful level 10/elite/ncaa gymnasts that struggled with them.
Also, it is very common...
For sissone (or any leap or jump to split), with from leg bent on a block, kick the back leg up to split. Also standing put the back leg on a block and lift it up and hold (even though that can be considered more from strength or control.
Any kind of kicks to splits would also work I guess
Not...
I have a problem with the single sessions being that long, we would usually start with 1,5 or 2 h, 3 times per week, which is no that different in the weekly total, but makes a different in the individual days. I have some new gymnasts in my group that moved up to 3 h workouts when they can from...
I won't put a 4 year old in a 4 hour workout, even if it has breaks and other activities, it is just too much, especially if they already went to school. Even for 6 years old I find it too much.
I usually just let go of them. Also offer kind of an open door if they reconsider (if that's something you think is good for your gym).
Our gym attracts gymnast from a couple of clubs nearby and usually they have a hard time with it. We've also had some gymnast leave for a couple of gyms, some...
I don't think Switzerland (or anywhere in Europe, west-europe, specifically) trains USAG. Many countries in Asia and America do, but I have never seen it anywhere in Europe.
Two things I like to do with that mount is going down to middle split or cartwheeling to one side (Anna Pavlova's style, maybe you are too young to know her, but you can look it up in YouTube)
It is perfectly possible. The level could be 2, 3, 4, depending on the skills and abilities of the gymnast. There's no petition needed because all of those levels can be entry levels, so no score/experience needed to enter.
If I remember correctly it is just Club Gimnasia Tres Cantos, but I'll try to check it.
https://www.clubgimnasticotrescantos.com/
One of the coaches is former Spanish olympian Alicia Fernández.
I'm not familiar with traffic and distances within Madrid, but looking at it, maybe the closest could be Tres Cantos or San Agustin de Guadalix that both have gym clubs. Tres Cantos has slightly higher level than San Agustin.