the part that is geo-blocked is the login, not the posting. any scheduler that posts through tiktok's official api sends the video from its own servers, so where you sit doesn't matter once the account is connected.
so the practical setup: your client connects her own tiktok account to the scheduler from her side (most tools have a "connect link" you can send to a client so she signs in herself and you never touch her password), and you post from india from the tool. no vpn, no second device, nothing that looks like a different-region login on her account. that last bit is what gets accounts flagged, not api posting.
on reach: posts sent via the api carry the same visibility as app posts as long as the account owner sets the privacy/visibility herself on connect. the "api kills reach" thing comes from tools posting as private by default.