If Regina could use magic in storybrooke, then surely she would have killed Emma by now. I think her magic has limitations in Storybrooke. Remember in the episode where Emma and Sidney were running against eachother for sheriff, and Mr.Gold made that big explosion? Regina freaked out because she thought Emma was going to leave her. Or maybe it was a different episode. I can’t remember.
I read somewhere that one of the actors or writers said that the curse could be stronger then Regina. Thats what could be keeping her from using magic and not just magical items.