You are misreading. MB was not with her before going to 11th, as he never left 11th all night. The only people who were with her in going to 11th (and assuming that the plural isn't simply an error) are CR (later in the night) and DR (earlier). MB is the acquaintance that watched her walk away.
No, I'm not misreading. I know MB wasn't with her before going to the BUILDING on the 11th and I believe you're interpreting the report as the first option that I pointed out. I can certainly see how it can be interpreted that way. However, it says "OTHER APARTMENT".
I was pointing out that I personally interpreted it as the second option -
"the acquaintances that were with her in going up to the other apartment on 11th" in THAT option would include CR and MB because they were both with her (presumably) prior to her going up to the OTHER APARTMENT (JR's).
One can consider "other apartment" to mean "other than Smallwoood" or "other than CR's". I would assume that since there is more than one apartment in question on 11th, they would word it as "the acquaintances that were with her in going up to the other apartment BUILDING on 11th". Since it's not worded in that manner, I take "other apartment on 11th" to mean the other one (JR's) which is ALSO on 11th.