Will my current insurance agent know if I purchase another policy with another agent from the same company?

Would the older agent be somehow notified if I purchase a new policy under someone else?

No.

Or would the old agent only have access to what I purchased from her previously?

Yes, this is correct. Unless you choose to tell her. At no time is G allowed to share your policies to different agents (happened to me with P-company).

When that happened, complain to PDPA, MAS

Hi Anon, of course not as client confidentiality is a very important thing for all FAs. You are correct in saying that the old agent will only see whatever policies you have bought from her or whatever you've told her about. And of course the most important thing is that you must trust that the new agent is doing the best for you.

If you're not happy with your old agent you just need to get your new agent to write up a letter which you'll have to sign and that's about it. And of course you can just ignore any messages or calls from your old agent.

I've helped service clients who have been unimpressed with their old agent services. You may wish to contact me if what I say makes sense.