What to do if i could visually see my vagina close and relax when i have a mirror & contract and release my muscles down there could this mean that they are strong?

Probably: this would only show muscle coordination not strength,usually if muscles are coordinated they are strong

Nl. vag. function: It just means that you have well functioning vulvo-vaginal muscles and just keep them this way for enhanced sexual pleasure! This may change after childbirth(-s)!

Yes: yes, if you can do this voluntarily and to its maximum possible potential.. yes..