There's a good chance that your ALO is in charge of more than one school. I myself am the ALO for 8 different schools. As well as any kid from those areas that may be home schooled. When it comes to which ALO for which school, part of it is where the ALO lives. Part of it is what schools need an ALO. It's also not uncommon for the bigger cities in a state, with multiple high schools, to have multiple ALOs, because this is usually where a larger majority of interest comes from.
In your case, she is definitely the only ALO for your school, but your school is not the only one this ALO takes care of. There's also times when ALOs might need to add or change out some schools; albeit rarely. Such as, if an ALO has some things happening in their life at the moment, and needs to get a different ALO to take care of a couple of their schools for that year. Or, like me and an ALO from a nearby city; we aren't allowed to be an ALO for any school if our kid goes there and they are applying to the academy that year. Last year, I had to take over a school from an ALO because his son was applying to the academy and he went to that school.
So, you don't have to worry that another ALO is sharing your school. It's just one ALO. But, your school isn't the only school your ALO is taking care of.