Where is the 'fun' happening? In your backyard.
Dogs by nature repeat behaviors that are rewarding (fun- satisfies their instinct to investigate/interact with their world ) for them, whether it is checking out the scents in the grass, a mouse has passed through, a cat walked this way, they can pick up on the scent and curiosity/ instinct will pull their minds away from their focus on you, or checking out that corner, there may be something new there today or what is that up in the tree. These are all 'distractions', especially for a young dog.
We often start in the house where everything is 'quiet' and familiar, and once the skill is reliable inside, we take it outside, and where what we thought they had learned often falls apart. Why? Outdoors can be highly distracting and dogs do not 'generalize' well, to them 'come' in the house is not the same thing as 'come' when they are outside, so when we change locations, and make it 'harder' for them, we need to 'start over' again and reteach the behavior we want from the beginning.
When you first go outside, try to give her a few minutes to check things out satisfy her curiosity a bit. Then when you want to start the session put her on leash, not to 'reel' her in, but to keep her from wandering away. Wait, be patient, for her to look at you, then toss a treat on the ground within the length of the leash, allow her to go get it, as soon as she eats the treat she is likely to look back at you, (if not, say their name, make a noise, whistle, lightly clap your hands to get her to focus on you) then cheerfully say your recall word - only once, take a step or two away from her, pat your leg, encourage her to come to you, lots of praise while she does, when she does (no matter how long it takes, or how far she has come) have a 'party'!! treats, praise, let her know how happy you are. Do a few repetitions, dogs learn best in short sessions that are fun, and then release her, let her go play. Give her a few minutes to do some 'dog things' then go to her, leash her up and try again. Once she is reliably 'coming' from a short distance, then you can give her a little more freedom by using a long line (or rope) to gradually increase/ manage the distance she can move away from you. Remember to practice in a variety of locations, by the back door, out in the far corner, by the tree or the back gate to help her learn that no matter where you are, when she hears that recall word, that 'sound' you make, means you want her to come to you. Remember that when you move to outside the yard, it is a whole 'new game' you will need to make it 'easy' for her again, up close, on leash, high value treats, encouragement from you.
Ensure you are using high value treats especially in the early (learning) stage, once she catches on you can mix it, substitute meaningful praise or/and an opportunity to 'play' or 'go sniff'.
Building a solid recall is a process, it is one of the most difficult skills for our dogs to become reliable with because we are asking them to put aside those things they 'naturally' like to do - to sniff, to chase, to play, to wander and follow their nose.