I was wondering if I need to see a therapist before starting HRT in the USA as someone who doesn't live there. I'll just be staying 90 days. Thank you.

You don't need a therapist but you will need a doctor that works under Informed Consent. The doctor will probably insist on blood labs though.
Since you will be here only 90 days, they might not even want to start with you and if you don't have insurance, things will get pricey.

Most doctors dislike being a pill pusher and would prefer providing the follow up care to ensure everything is going according to plan. In addition, often people are stated at a lower dosage to see how their body responds and then latter, possibly 90 days the dosage is adjusted upwards. You might find a doctor willing to work with you but I suspect you will have better luck if you seek out a doctor who can provide long therm care.