My ds1 had a problem with the "j" sound till he was about 5. We spoke to his teacher about it, who said it was quite normal at that age to still have some sounds which they struggle with, but to wait a year and she would then recommend referral to a SALT if things hadn't improved on their own, but she thought it was not a good idea to jump in too early as it could as you say, damage his self-esteem. As it happens, a year later, things have improved on their own. I think for some dc's it just takes longer to manage the full range of sounds than for others.
The only thing we did was get a hearing test for ds1, to check that wasn't the reason he couldn't make the sound properly.
We didn't do anything to help him with it in particular, we just tried not to draw his attention to it. I don't think it is necessarily linked to learning problems (ds1 is classed as "gifted and talented", so really no problems there - not that that is intended to be bragging). I'd wait till she's in full-time school and ask her teacher, as I say, we were told it was quite normal and school had no concerns.
My dd3 - age 4 has loads of problems with her speech and sees a SALT. Her probs are quite unusual and in her sessions the therapist has said she is happy with certain, more common mistakes like the one you describe as this will make it easier to be understood when she starts school. If your SALT says it's ok then it will prob sort itself out. Just as others have said - say it correctly without making an issue of it. you will prob find her friends can understand her - I know most adults can't understand my dd but her friends 'translate' at preschool. I am hoping they will be in her class at school to help her teacher! hth