My 2 cents worth from a slight different perspective...
Our gym is a bit more lenient with the younger and lower level kids when it comes to "slacking off" in conditioning. Even though they spend similar amount of time doing it and part of the time doing it together (especially in the summer when conditioning is much more frequent and intense), understanding the circumstances the coaches are never as hard on the L4/5s so long as they are showing progress. My feeling is that your gym is no different.
Sometimes it could be the young gymnast herself who might be trying too hard to keep up. In more ways than one, that's a good thing! Also, conditioning with the higher level is a good thing as well because not only is it good for harmony, it's also getting the younger ones used to what's ahead in the future. Strength and stamina (including cardio) is absolutely needed for L6 and up. Just spend some time explaining that to her (or communicating that feeling with the coaches) and she'll be fine. Also, if she has the will, she will be able to keep up in no time. Bear in mind that although conditioning (along with dancing) is a big part of competitive gymnastics, only a few gymnasts regardless of level are willing to participate if given the choice.
BTW, I would recommend not watching her practice right now until she's more comfortable with the conditioning. Otherwise, you could be heart broken watching her "struggle" through it. If you do any intensive exercise at all, you will understand what I mean. I was watching my 10yo L4 going through this a couple of weeks ago. From the look in her face, a big part of me was wondering whether she will pass out due to fatigue or dehydration. Then I saw the other kids whom she was running along side with and who handled it well, I have no doubt that she will too in time. Besides, as soon as she stepped out of the gym, she was full of energy again.