Such an old thread this is!
While many in the west have lost sight of true yoga, there are little gems out there with small classes that are more spiritual as opposed to athletic. Those classes (in my experience) have very devoted students who come to yoga for the right reasons.
And Melinda on to your strap issue. Did you discuss with your teacher your injuries? And what pose did the teacher have you doing with the strap? Was it Supta Padangusthasana (reclined big toe pose)? To be honest, I can’t understand why the teacher did not give you an appropriate modification or another pose to do while the others were doing the pose with the strap. But with that being said, straps can be a very useful tool for those students who are tight or have certain restrictions. An example using the above mentioned pose: If a student has tight hamstrings and comes into the pose using their hands to lift the leg, they will likely pull their leg up to 90 degrees or close to it. BUT, the knee will be bent. This will not lengthen the hamstrings. Using a strap will allow you to back off the 90 degrees but keep a straight leg, thereby giving you a better stretch of the hams. A strap or any prop is not meant to take you past your normal limits, but to get you to where you will benefit from the pose. A good teacher will know their students limitations/injuries and provide variations/modifications, with or without props. As I was not privy to what occurred in the class, I can only guess.
And perhaps Melinda, vinyasa flow is not the style for you. Have you tried other classes with other teachers? Not knowing the extent of your injuries, a yoga therapy class or a more traditional hatha class might serve you better.
Looking forward to your response.