Does she whine before she goes? Does she poop outside AND poop in her crate (you said she waits until she gets in the crate to go). Sometimes if you bring dog inside immediately after they go, they'll learn not to go if they want to stay outside. I doubt that's what she's doing, because she's so young and you haven't had her very long. Take her outside and give her a command (go potty, go poopy, etc) and when she does, praise the heck out of her. If she starts to go in the house (or the crate) and you catch her in the house, pick her up and quickly take her outside and give her the potty command. If she goes right away when you put her in the crate, you might have to wait there a minute and if she starts to go, then pick her up and wait with her outside until she goes. If she's going in the middle of the night, then you might have to wake up a few times to take her out.