Let's just look at this timeline.
MB began dating HW several weeks before Evelyn went missing, so maybe in October. When asked where the baby was by him, she supposedly told HW that Evelyn's dad had 50/50 custody and she was with him (not true according to police who say SHE had full custody, and dad is a few states away). According to HW he never saw the baby (photos that are supposedly HW with the baby have been disputed as being ANOTHER young man MB briefly dated, but who knows). This makes me wonder where Evelyn really was when MB was spending time with HW during October, November, first half of December.
If Evelyn was taken sometime in December by AB or whoever, it sure seems odd that MB would just continue dating HW, change her last name on social media account to his last name, sell her 2018 Cruze car, all while NOT crying or freaking out to any friends about her missing baby. Then when a very upset grandpa finally calls the cops because he hasn't seen his grandchild in months, MB says "I'm a little worried about Evelyn since I haven't seen her in 2 months" and gives inconsistent stories to police.
I don't think this is rocket science. Sure, there's a slight chance someone else took Evelyn, but even then, it's like MB didn't much mind. JMO