documents for visitor visa application

[adr]

I wish to have my mother visit USA in October on B2 visa.

1. Should she apply for visitor visa right away? She will be applying to Mumbai consulate.

2. On the webite where it lists documents needed for visa application, it states that:
If you are travelling to visit your child legally residing in then US, then additional documents recommended.
Child's legal status copy.

Does this mean that for applying, I only need to send a copy of my passport (all pages) and green card? Or should I send any more documetns?

3. We were told that some travel agents block the appointment slots and hence can get an appointment quicker. Is that legal?

[immihelp]

1. You can apply. Appointments themselves can take several months to get now.

2. Read https://www.immihelp.com/usa-visas/visitor

3. That's not true. That is illegal as well.
Appointments are blocked by passport numbers that can't be changed later. That means, appointments are not transferable.