I haven’t really been following this, but I thought it was nothing to do with her moderate ness and everything to do with the trade barrier between NI and the mainland.
I think it is a combination of issues. Certainly the whole Brexit/NI trade barrier is a huge issue, but she is also seen amongst some in the DUP as not being socially conservative enough for their liking.
We might end up with a situation where she is kicked out as DUP leader but could remain as First Minister - now that would be interesting.
Actually this is really worrying as I think it is a manifestation of wider unrest amongst the loyalist communities in NI and a new leader, without being shackled to the Brexit deal, could be more outspoken against it and, by inference, provide legitimacy to those that want to use non peaceful means of protest.