Thanks for all the responses guys!
She does get a lot of inside time, when we are home she can come in for most of the night and also sleeps inside in our room. During day times, I like to keep her outside. This behaviour has only started in the past 2 weeks so I am unsure if something has brought it on?
I have tried giving her extra toys, toys that also challenge her (to hopefully keep her focused), giving her a bone for the day, and also taking her for a nice long walk before she is going to be put outside to tire her out.
We have 6ft high fences, and you cannot see underneath them. It just seems once she's had a glimpse of what she can get up to once she is out, she is only going back for more!
When we go out somewhere and Missy needs to travel in the car, I can open our front door and she will walk calmly next to me (with no lead) and sit and wait at the car door. She is usually very good when it comes to going out the front and will not wander off from me.
The backyard - we have her trained that in the morning once waking up, she will go and sit at the back door to let me know she needs to go, and then will usually go outside and do her business then sit at the back door to let me know she is finished.
We start obedience training in February (that's when they are doing their first inductions for the year). I am hoping this helps calm her a bit. We also socialize a lot with other dogs during the week and every weekend.
Missy is registered - This was one of the first things I did when getting her! I didn't want any issues to come for not doing so.