This.
@MzLyn you said yourself she is "JLo thick" - if she's only 11, my guess is that her coaches can see that she isn't going to be able to fly forever. Sooner or later she's going to have to be a base. Might as well learn now, while she's still eligible for juniors.
As others have said, please don't encourage this in your daughter. Whoever said it's toxic is dead on. And if she's hearing it from you at home, believe me, she's embodying it at practice.
**To be perfectly blunt, it's not up to you what she does. I'm confused as to what you're asking. Are you asking if you should demand that she fly because you're not comfortable with her basing because of her upper body strength? If that's the question, then a thousand times NO.
***If you're just asking what to do, then you have 2 options: either pull her from cheer or figure out ways to build her upper body strength (one of which is basing... She'll get stronger very quickly if she puts in the work at practice - but if you're genuinely concerned, there are plenty of ways to build upper body strength)
****Oh. Your third option is drop her off at practice, go to Starbucks, and let the coaches do their job.