My girlfriend just suddenly doesn't want to spend time with me?

Well my girlfriend and I are both 16 and we haven't had too many problems. We have been dating for almost 10 months and all of the sudden she starts thinking about how much we think differently. It really hasn't caused a problem for us. For example she is a Christian and I'm an Atheist. She thinks it will become a problem later but I told her she is free to worship God and go to Church whenever she wants and it won't get in the way. She always seems to want to take a break but we don't in the end because we get our feelings out there and we fix the problem. But every time we have even the smallest of fights, like buying her very disobedient dog a shock collar. She was open to it at first but then she said no when we actually zapped him (please don't comment on this story please. I get enough of this from her family). They returned it a day later and didn't give it a chance. I felt like I wasted my money on it and I told her to give it a chance and she stopped talking to me for the day. Now she doesn't want to hang out with me. She only wants to go to the beach and hang out with her family. I understand family time but she hasn't wanted to see me in 3 days but we still talk which is enough for right now. I am trying to give her the space it seems she wants. My girlfriend does seem to have a short temper and when I try to talk about if she likes other guys she thinks I'm accusing her of cheating and being a whore. It's really hurtful when she says that kind of stuff when I'm not accusing her of that. She also seems to be attracted to the guys with muscles and a six pack. She also complains why I'm not like that. It seems like she wants me to be who I'm not. I'm skinny and trying to workout and become something like her dream guy. I'm starting to look more muscular and she seems to be more attracted to me but she is more attracted to her guy friend who has muscles. I know I can't stop physical attraction but I don't know why she is trying to make me into the worlds next Taylor Lautner.