I'm glad to hear that the teacher knew that she was being harsh on Becca. Just because a child is not working up to expectation is no excuse to say insulting things to her, no matter what. But, teachers are people too.
Please follow up on the specialist, and if your child continues to lag behind in her reading, insist on an evaluation. My son is LD, which is not a horrible thing, but the schools never evaluated him until it was too late. I didn't know about LD at that time, and my son suffered for it. If reading disabilities are not addressed in the first three years of school, the person may never read at their age level, even into adulthood. It is imperative that these things be diagnosed early for the sake of the child's future. A quick and easy home test that may help you know if dyslexia is a cause of hindering your Becca's reading is to ask her to rhyme. Ask her for a word that rhymes with an easy word, like bee. If she has difficulty sorting out the sounds so that she can substitute another sound at the beginning of the word, such as me, please request that she be evaluated for LD. This is not a substitute for a professional evaluation, but it can give you a clue. Don't take the word of the school that she has to be a certain amount of years behind to be evaluated, that's just not true, nor is it the law. There is a Federal law to help children in school who have disabilities, and the schools have to follow it.
How do I know? I had to fight for services for my son from 2nd grade through 12th grade, and it was a hard fight. I became the mother they hated to see at meetings, but I eventually got what my son needed. My son, now 23, is successful, loves to read, and his reading and writing are getting better every year. It was well worth the fight, because he now can survive in a world that is so very reading-based. Anyone who wants links to resources feel free to contact me.