I'm sure you remember a lot of what you learned during med school and residency and intellectually would be able to complete your residency successfully. The trick is to convince your residency program or another residency program to give you a chance. I imagine their first question would be whether the reason you quit still exists (motherhood, illness, disillusionment with specialty or with medicine, etc.). Then hopefully they would give you full or part credit for the time you already put in. I don't think you would have to relearn everything. The skills you had already mastered should come right back. You could spend some time now making sure that you are up to date knowledge-wise.
I don't know of anyone who has returned after a long break during residency, but that does not mean that you can't do it! I think one of the biggest hurdles to re-entry is self-confidence. The longer you are away from medicine, the more impossible it seems to return. But once you are back taking care of patients, those feelings should resolve pretty quickly. Be brave!
I took a long break during practice, so feel free to PM me if you would like more details about that.