Someone on that FB page is suspicious because the mother is referring to Mariah "was" not "is". That is not suspicious behavior in and of itself. I think that happens quite often.
IMHO the context makes a difference, and also how long after someone has disappeared.
Three years after someone has gone missing, then loved ones are often going to say 'was' even if they don't know if the missing person is alive or dead. I think it's a cross between accepting what they believe is the inevitable, and also the context is that everything about this person has become past, and therefore past tense language will be used not just in context but in any context.
We're talking about 24 hours, even less than 24 hours. Unless the mother is extremely suspicious that the child is deceased, then I think it's only the out-of-context past tense language that is suggestive. I'm playing the video over and over trying to work out context, and I'm finding it tricky. Talking about past events is going to produce past tense language. So, to paraphrase, she was born after a tubal ligation, therefore she 'was' a miracle. This is a past event so I think it's 50/50...but as I type this I'm verging on a desire to say that it should be that baby 'was' born after a tubal ligation, therefore she 'is' my miracle. And I need to play the video another dozen times to figure out where the switches from 'was' to 'is' happen exactly in the sentences, bearing in mind that this is a woman who is obviously emotionally fried.
I am seeing things in the words that throw up red flags for me. First is the word 'angel'. Kristy also says something about wanting to see the child's smile...but she doesn't really finish the sentence, which leads me to think she's possibly saying that one day she'll see that smile again [when they meet again in heaven?]. Is that cruel of me to wonder that? I am trying to be dispassionate.
"This girl" ... it's not just a tendency to use terms of endearment in Kristy's pleas, but "this girl"???
Also, the first statement I read from Kristy was full of Kristy/me, me, me, I, I, I. Very little about Mariah and how Mariah might be feeling. I'm not hearing things like "I'm terrified for my little girl, she must be so scared"...the statement was just a list of "I" statements about Kristy.
My non-expert conclusion would be that Kristy might suspect what has happened, that she strongly suspects Mariah is deceased, and she has a suspicion of who caused that.