Agree. During the initial searches through the night they had all but eliminated vehicle accident (of which was their initial thoughts when Tom missed curfew). By the next morning, with vehicle accident ruled out, the next thought may be suicide. This was Canadian Texas .... if they were in Chicago or Houston the next thought may have been foul play but foul play does not immediately come to thought in quiet small town Canadian. So, with emotions and fear running high along with some family history, PM naturally would think suicide might be a possibility.
As you point out, if PM was currently covering a suicide then WHY would she respond to NL that suicide came to mind? She would not.
IMO, far too much has been made of PM's very early response the NL's question.
In TB's Body #2 timeline and who interviewed who are a bit different.
When the M's originally contacted SO office, they were told "He's 18, he can do as he pleases.
The 2nd time they called, Deputy Pine came out to the house (time unk) and the 3 of them stood outside of the M's house and talked for 15 minutes. (Don't know who the 3 are).
Two days later PM and CM went into the SO's office where they were interviewed by S.O Brit Clapp (sp) and a State Trooper.
PM mentioned suicide and "the choking game" Suicide was not out of the realm of possibility. PM was adamant that she had seen no behavoir changes in TB. She also mentioned that maybe he ran off to Wrestlers school.