Ok it sounds like your coach is unprepared to take a child alone to a session.
I've actually never heard of that happening. Do they have higher level gymnasts? Because unless it's a massive club then by level 8 you are sure to only have 1-2 girls in a session at the bigger comps.
How many girls are there in the level.
The first two are individual comps (though how can he guarantee the other girls will be in the same age group as who is a junior and who is a senior is only determined after entries close for both of those comps. The girls must be a lot younger for him to be so sure. How old is your dd that he is certain she will be a senior?
As for the top 6 thing being the team - that would only apply to state clubs. And there are no age divisions for state clubs (all mixed teams) so she should have that position on the team.
As for it being too expensive. Do you directly pay for the coach for a competition? Do you have affiliated judges (I'm not sure what the current policy is but it is likely to be if you don't provide a judge for each session you have girls competing you have to pay a $100 fine).
But I've not heard of a club not allowing a girl to compete because they are the only one in a session or directly passing individual costs onto a child (usually you pay an extra say $20 per comp on top of the entry fee and that covers everyone competing - so some comps they might have 10 girls in a session, some only 1, but you pay the same extra - usually you wouldn't even know the amount as it's just a single comp entry figure you are given.
But I'm sure it has been done where individuals are charged their cost but seems an odd and very unfair way of doing things.
One other thought if he is using the terms junior , intermediate, senior then I think he is incorrect as I'm pretty sure for level 5 this year there is only 2 age divisions (not predetermined) and mixed groups for state clubs. The divisions he is mentioning are not current.
And one more thing - are these girls really high scorers? As only the top 160 girls from the qualifier (and country champs) are selected to state so he can't know who qualifies until after the July comp.