Leaky valves are really quite common OP.
If you think or circulation being like your central heating at home then the heart is the boiler and has both mechanical parts (atria, ventricles, valves) and electrical which is what is seen on an ECG.
A mild leak shouldn't be of much concern, they will continue to check it is not increasing.
The right side of the heart takes deoxygenated blood from the body and pumps it to the lungs to oxygenate the blood.
The tricuspid valve is between the right atrium and the right ventricle, the pulmonary valve is between the right ventricle and the pulmonary valve.
Heart valves can be replaced but no one wants to put a 15 year old through that without good reason.
The first pacemakers only had one electrical lead and that was fed through the veins into the right atrium and then in to the right ventricle. Obviously passing a wire through the tricuspid valve means it doesn't close properly and therefore has a small leak.
Modern pacemakers often have more leads, but many pacing leads are passed through the tricuspid valve everyday.
I am not saying your DD needs a pacemaker, just that small leaks are not always a problem to the extent that causing a small leak is preferable in some procedures.
The British heart foundation has a lot of easily accessible information https://www.bhf.org.uk/
I know it is pointless for me to say try not to worry, you are a parent you will worry. My advice is to have a look at the BHF with your daughter. Together compile a list of questions to ask at her appointment.
Step away from Dr Google.