Phonemic awareness should be mastered by second grade. However, if your daughter's teacher caught the weakness now, that is a good thing. It is never too late and actually playing games to increase her phonemic awareness can be fun.
Phonemic awareness is the ability to play with and recognize sounds. Keep in mind this does not mean letter recognition - just audible sounds.
The first thing that you need to do is have your daughter's hearing tested. The school may have done this or can do this free of charge. If they detect a problem, then you can have it test by a professional. You want to make sure that there is no physical problem that is getting in the way.
Some phonemic awareness activities are reciting nursery rhymes. Listen carefully as she recites them. Is she saying all of the world correctly? Can she say which words rhyme? Tongue Twisters are another way to get her to play with sounds.
Another exercise you can do with her is to ask her what sounds begin certain word. (Remember you don't want her to name the letter you want just the sound.) For example, if you driving in the car, as you pass by places, name the place and ask for the beginning sound. So when you go pass a Target, your daughter would say the sound /t/. You could also say gas station and she would say /g/. You can flip roles around where she says the place and you give the sound. Get some wrong so you can test to see if she is really hearing you.
If you want to get some physical activity, try jump rope jingles. Once again this is just sound play.
Play the rhyming game. Take turns selecting a word and see how many other words you can rhyme to it. Continue to listen carefully as she rhymes to make sure she is hearing the sound correctly.
Have her break down the sounds in a word. For example you say "dog", she would say /d/ /o/ /g/. Remember we are listening for sounds, so if you said "blue" she would say /bl/ /oo/. This will probably be a bit more confusing for you at first, but it is an important skill.
Say two words and ask her if they rhyme. For example "top" and "flop", she would say yes. "run" and "ran" she would say no.
Ask her how many syllables are in a word. For example you would say, "swimming" she would say 2. "vacation" would have 3. You can snap or clap out the syllables making the activity multi-sensory. You can build on this by saying the word and having her break down the sounds.
The last idea I have for you is more advanced. You would say a word like "rainbow". Have her repeat the word. Then ask her to say the word again without "bow" She would then have to say "rain". Another example is you say "dinner", she repeats the word. You ask her to say the word again, but this time leave out the "ner" part. She would say "din".
Hope these activities help your daughter. If she is still having difficulty at the end of the summer, I suggest having a conference with her new teacher. Give her the background and tell her that last years teacher thought she might have a learning problem. She can then start the paper work to have further screenings done.
Enjoy spending time with your daughter and make it fun!