I highly doubt any lawsuit of this nature would be anything close to a slam dunk, especially in Texas. I'm not finding any federal court cases that provide legal precedent on the topic, and Trump revoked the Obama administration guidance that trans people are protected under Title IX.
It would start in a state court and progress to the state level Supreme Court, I imagine. After that it goes to the federal SC. This would be preferable if they are seeking punitive damages.
Or I guess they could appeal it to the federal level. This is the route if you wanted to make a precedent for the entire US.