Don't be concerned if she dallies a bit before coming to you at times. She is going to get more and more involved in the world outdoors and you'll become less and less interesting. So long as you have at least reasonable control over her, you're doing OK. She's at a tough age (3 months), where she's too young for negative reinforcement, but old enough to be somewhat independent. If you aren't able to enforce a recall ("come") command (e.g. you can't catch her), it's best not to use one. Instead, say something like, "over here" or "this way."

If you keep repeating a command you can't enforce, you're just teaching her she doesn't have to obey it. The golden rule is, "Never issue a command you cannot or will not enforce."
 
I'm really glad to hear you are not over-handling her on your off-lead runs and are allowing her to explore and develop her hunting skills. Many new puppy owners get fearful if they can't see their puppy, which is often when you are in tall grass or the woods, and constantly call the puppy to them. I refer to this as "nagging" and the result is generally a puppy that starts to tune you out. Continue calling her only when it's necessary and she should continue to respond well. 
I must warn you that at about 5 months of age, she will become much more independent and the day will come when you will see her make a conscience decision *not* to come when you call. That's the day you start getting her conditioned to wearing the e-collar and about 2 weeks later you begin training her to come with it. 
It's extremely important that when you do train her to "come," you make sure she comes all the way to you and you touch her before she is released. If you train "come" as a hard command - one that absolutely must be obeyed - it will make the rest of her training easier. For one thing, it will help immensely with retrieving.