You did really well if you had her off leash prior to 7 months. Most folks, myself included, don't even try to get them off lead prior to that. What she's doing is perfectly normal and to be expected. She's becoming an adult and her prey drive instincts are kicking in. She was purpose bred to do exactly what sh is doing.
First things first;
You need to put her on a "check cord". A check cord is nothing more than a long piece of 1/4" rope with a clip on the end. 1" wide canvas web works well also. I would start with a 30' check cord. Attach the check cord to a harness, if she does not have one, now is the time to get one. I would highly advise not to clip it to her collar. She is going to hit the end of the check cord from time to time, and you don't want all of that pressure on her throat.
Start her out with the check cord attached to the harness with maybe 3'-4' of length between the collar and the check cord in your left hand, let the excess drag behind you.
Start out at a walk and enforce the "heel", then let her range out by allowing the check cord that is dragging behind you to slide through your hand.( I highly recommend a light glove here, that rope can abraid your hand witth all the dirt and grit it will accumulate.) As she gets maybe 15', give her the "whoa' command, or "easy". Don't let her pull. She pulls, you stop moving, turn around and walk in the opposite direction, until she gets back in front of you.
Periodically stop and command her back to you. She doesn't respond, give a gentle pull, and some encouragement. She still doesn't respond, start to reel her in to you. You do not move, she comes to you. Give her lots of encouragement, and the moment she starts to come on her own, stop reeling her in and let her come to you. Repeat this alot.
Once she's out front and not pulling, Command "Stay" and walk toward her while pulling the check cord back through your hand. If she moves one iota, while you are walking toward her, you pull her back to the point where the "Stay" was given, while simultaneously taking up the slack in the check cord and walking up to her. Once you get to her, start out at the heel and repeat.
Once she understands that she is on a check cord, you can move to a longer cord and go back to the field. Let her go and keep working on the same drills, over, and over, again. You can even drop the check cord, if it's long enough, and you have the ability to get to the end and step on it if necessary, and let her blow off some steam first. Sometimes that really helps a lesson.
What you are doing is called "extending the leash". You are basically imprinting in her mind that you can enforce a command, regardless of the distance. She doesn't know the difference between 15', and 150', she just understands that you can make her do what you want, and will ultimately come to accept it, or you up your game to an e-Collar.
All hunting dogs are started on the check cord, so don't internalize this as a failure on your part that you have to use it. The check cord is an integral component to training a bird dog. She may eventually need and e-Collar, but right now she is to young. Work her on the check cord.
Lastly, seriously, seriously,consider an invisible fence system for your house. They are a wonderful development for dogs. I cannot recommend one enough.
My current puppy, Finn, is 13 weeks old, He's been on a check cord now for 3 weeks. We just started forest walks last week, and longer retrieval training on a 100' check cord. He'll be on a check cord for many months to come. Hopefully, by summer, I can get him off the cord in a controlled environment.