Yeah.. I mean, I do agree that there is a way of saying things. It's hard to analyze the situation without knowing Beth and her life. It could be a variety of things. She could honestly think what she is saying, or she could just be frustrated about something else and be taking it out on you.
If you really feel like it is worth it and your heart is in it and you are just ready to push on, just kind of think of it as an argument and keep doing what you are doing. But don't be afraid to stand up for yourself. That doesn't mean you have to be ruuuuude,but don't let anyone discriminate against you and give you crap that you don't deserve. Even if it's just a simple, "you know, I work really hard for you and I don't think that was a very nice comment." That sounds actually disrespectful, but you get what I'm saying. If she is being unreasonable, try to speak to her about it.
I would suggest trying your hardest to develop a good strong relationship with your trainer. Trust me. It makes the world spin smoother.
Good luck. Say a prayer. I hope it goes well.