This may sound wrong to you (It did to me when I first heard it) but when she goes inside it's important not to react, any reaction will reinforce her fear. Growling is a form of chastisement too.
I dare say someone with good intentions has trained her by reprimanding her for going inside from a very young age. In many ways this is like reprimanding a 6 month old child for soiling it's nappy.
Dogs remember things that happen to them at an early age and carry those early lessons for life, it's called imprinting. She could have been imprinted with fear associated with going inside and that will be hard to overcome.
A few others will have other Ideas but I think you are just going to have to toilet train her all over and the only feedback she should get should be positive feedback for going outside.
Like Newfsie wrote, keeping her close will be important so you can keep an eye on her, but with young children around it will be tough (I have young kids and they are very demanding)
She sounds like she is a great pet so it will be well worth the effort.