You are correct.  Their body function muscles are not strong yet.  You need to take her out on a leash, more often.  We hung a bell on our backdoor knob.  When Maggie needs to go out, she rings the bell.  I tell her "I'm Coming". She dances while I QUICKLY pick her up, attach her leash and out the door we go. We have a fenced yard, but attaching the leash tells her she needs to hold it until the door is opened.     
				__________________  "My Furkids" Maggie, Molly and Meme...     |