Hey J.,
I was a preschool teacher for a few years before I had kids. I taught the 3 yr. old class, and let me just start by saying that LOTS of kids came through my room who were having a hard time talking, or a hard time potty training, or a hard time learning to stay on their mats when they slept.... etc....
As a teacher I adored my class and I noticed for most of the kids that after a few weeks/months of being around their peers, those problems cleared up.
If she is speaking with a particular speech impediment (such as a lisp, the inability to pronounce a certain letter, or a noticeable impediment that is consistent with the way her mouth moves improperly) then someone may suggest to you to look into it. But that doesn't mean she needs some kind of intensive therapy, or that you should immediately place her with a speech therapist. In my opinion she's actually a little young for all that. If by age 5 she's still speaking with a certain impediment, I'd take her to a speech therapist.
But if she just doesn't talk much yet, or if she mispronounces lots of words... I'd tell her teacher your concerns and then work with her at home on extremely clear pronunciation when you talk to her. And also - talk a lot. I mean... chatter her ear off. Talk to her in an adult conversational voice and with adult words... tell her what you're doing as you do it - "And now Mommy' putting dishes into the dishwasher to get them clean..." and occasionally hold up an object and clearly pronounce its name, "PLATE"...
It will drive you a little nuts. So do it in moderation. I'd even get some flash cards - they're like $2 at Target - and go through them with her, pronouncing the names of the pictures clearly.
I bet after 6 or 8 weeks of being around other kids, hearing you talk about pronounce, and hearing her teacher do similar... you'll see a big difference!
Remember too - she's still a toddler. Lots of things are going to take a little longer than normal, every kid is different and she just might be taking her time.
And hey - worst case scenario, she actually does have a slight speech problem, in which case you'll (probably) Google it, find out ways to help her, possibly put her into therapy and a year later notice she doesn't really need it anymore. The important thing is that you're watching and ready to do something if needed.
Good luck!