If she's in a public school, I'd consider going ahead and asking for an evaluation. I've done it with my own son, and the experience was pleasant and painless. Nobody at the school made a big deal of it.
But there are things you can do with her to help her with /l/ on your own. In my pre-child life I taught English as a second language, and many of my kids had trouble making the English /l/ work for them. For what it's worth, here are a few of the practices we did that seemed to help.
First, make sure she can actually hear the /l/ sound well. Ask her to tell you same or different with contrasting pairs such as rot/lot, wit/lit, wet/let, red/led, peel/peer, dear/deal, and so on. (Find contrasting pairs with r,l, and w, since those are the sounds most often confused.) If she can identify when you are giving her a contrasting pair instead of a repeated word, then ask her to identify which one of each pair has the /l/. If she can do all that easily, then hearing the sound is probably not the problem.
Then teach her where in the mouth the /l/ is made - just behind the teeth on the gum ridge - and get her to practice putting her tongue there. A fun way to do this is to give her a lifesavers candy to hold in that spot with her tongue. Then practice /l/ sounds with rhymes and tongue twisters, slowly at first, to practice being aware of the tongue moving up to that spot and touching when we say /l/. Look up the Sesame Street song (from years ago) with Ernie and Bert that starts "La la la la lemon" - you can find it on YouTube. It's cute, and funny, and great practice to sing. Also, gather a box full of things around the house that start with /l/ and use them for a "what's in the box" guessing game. You can either give hints, of have her reach into the box without looking and feel the items and identify them. Games like this are a way of practicing without being obvious.
Finally, if you think she can pronounce the sound but is not yet incorporating it into her everyday speech, you can gently force the issue by "not understanding" when she mispronounces words with /l/. I would only use this tactic if I were quite sure that the mechanics of /l/ were now working for her. I did this for a little while with my son, who had /r/ trouble. He had shown me he could say /r/ clearly, but was still not using it in conversation. I would ask him to repeat what he had said, or I'd ask," Did you mean 'white' or 'right'?"
I hope you find this useful.