Panic on the front porch

Today was a pretty normal day until we got back from a trip to the grocery store. When we got out of the car I took Brittney, a handful of groceries and Jason's keys with me to unlock the door. Jason was right behind me with his hands full. I came in, set my purse and Jason's keys on the counter and took Brittney over to her toys so we could go get another load. I told Brittney I would be right back and she seemed fine with that. I walked downstairs and as I got to the car Jason came back up with another load. There was not even 20 seconds between the time I went outside and Jason TRIED to come inside. It was then that we discovered that BRITTNEY HAD LOCKED THE DOOR!!! I think when I left she tried to follow and open the door and when she couldn't pull the handle down enough to open it, she thought it was locked and so she turned the lock thinking she was unlocking it. It is important to note that Brittney NEVER plays with the door or the lock. I have never once had to ask her to leave the door alone. I know that she's tall enough to open the door and touch the lock, but it has never been a concern because she just leaves it alone.
Anyway, we had nothing with us that would help open the door. Jason's keys and my purse with my cell phone and keys were on the counter. Of course we never made copies of our key to give to our parents for an emergency. It was also 9PM and the office had long since closed. Initially, Brittney was there at the door and we could see her pulling down the handle and we tried to tell her to turn the knob on top of the handle. She soon lost interest and went over and played with her toys. We tried everything! We tried knocking, I asked her to come help momma, I told her I had a treat from the store but she wouldn't even come over to the door. We knew the window was locked so all we could do was talk to her through the door. Pretty soon I started to loose it. We were dripping with sweat and had melting, thawing groceries and I just felt so helpless! I was worried that if we didn't get in soon, Brittney would start to panic and cry and I knew if she did she'd never be able to help us then. My voice had gotten edgy and panicky so I don't know if she was afraid she was in trouble and wouldn't come to the door or what. Of course I knew that this was just an honest mistake and I wasn't mad at her, just frustrated about the situation. I knew we were making a ton of racket with our calling Brittney through the door and the pounding/knocking to get her attention. Our neighbor next door had come outside and asked if she could call maintenance or something for us. I wasn't sure if we should call maintance (or if they would even respond) or a locksmith or the fire department. She talked on the phone for a minute to someone and we were about 2 seconds away from making another more urgent call when I thought to ask Brittney if she wanted to go to Nana's house. She of course said yes, so I told her to come open the door so we could go. Finally I got her over to the door and she started yanking on the handle and again I told her to look on top of the handle and unlock the door. I heard her try a couple of times and I was so afraid that she'd loose interest and, with the attention span of a 2-year-old, walk away again. She tried a few more times and FINALLY I heard the click we needed and the door was open. We thanked our neighbor for being willing to help and went inside so thankful to finally be in. We told Brittney she did a great job by opening the door for us and rewarded her with some Nemo fruit snacks we got just for her at the store. It took me a long time to relax after we got inside. I did not like that feeling of helplessness! It was only about 12 or 15 minutes that we were stuck outside, but I swear it was the longest few minutes of my whole life. So, in 20/20 hindsight, a note to us: make a copy of our house key ASAP and wait to go back out to the car until the other has already come inside! We will not do that again!!!