Admission and credit are two different issues. These appear to be getting confused somewhat.
Regarding admission, MIT accepts many applicants with advanced mathematics skills that exceed the level of BC Calculus. Some exceed it by quite a bit. Having an advanced math background is certainly no detriment to the MIT admissions process, assuming grades are adequate.
Credit is a different matter. MIT automatically grants 12 units of 18,01 (Single Variable Calculus) credit to freshman or transfer students who have received a 5 on the AP Calculus BC exam:
The appears to be the only situation in which MIT automatically grants math credit based on prior coursework. However, MIT also allows students to get credit for several math courses by taking and passing the corresponding Advanced Standing Exam (ASE). These include 18.01, 18.02 (Multivariable Calculus), 18.03 (Differential Equations), and 18.06 (Linear Algebra).
http://math.mit.edu/academics/undergrad/first/advanced.php
It does not appear that MIT will grant credit beyond 18.01 for any previous coursework; a student must take and pass the ASE to get credit for 18.02, 18.03, and 18.06. A student who has taken advanced math well beyond Calculus I but who doesn’t have a 5 on the AP Calculus BC exam will still need to take the 18.01 ASE in order to pass out. That appears to be MIT’s way of ensuring “quality control” - simply having taken a course does not necessarily imply mastery of the material to MIT’s standard.
In the case of @anitram’s daughter, I am fairly sure that having taken Multivariable Calculus, Linear Algebra and Discrete Math at the local Community College did not impede her application. I’m also fairly sure that any “credit for some of it” that she got was a result of taking and passing the corresponding ASE exam.