All you need to do is email (reservations should have an email address on their website) and ask if they are guest friendly:
Hello -
Is your hotel guest friendly? I will be having a ladyboy friend stay with me.
Sincerely,
John Monger
Make it a point to mention that your guest will be an LB. Virtually every hotel in lower Sukhumvit is LB friendly, but a handful will charge the "guest fee" scam. Good luck.