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Senior party colleague and East Antrim MP Sammy Wilson said the allegations were a “bolt from the blue”.
He gave his full backing to interim leader Gavin Robinson, insisting the DUP should not be distracted by a leadership contest at this time.
Lagan Valley MP Donaldson quit as leader and was also suspended by the party.
It is understood he is charged with one count of rape, one count of gross indecency and several counts of indecent assault.
It is further understood that in a letter to party officers informing them of the allegations he made clear he would be “strenuously contesting” all the charges.
The 61-year-old will appear in court in Newry, Co Down, on April 24.
He travelled to London on Friday after leaving Antrim police station on Thursday night.
A 57-year-old woman has been charged with aiding and abetting offences in relation to the same
East Belfast MP Robinson, who was DUP deputy leader, was unanimously appointed interim leader in an emergency meeting of the party hierarchy on Friday.
Wilson said the party now had to regroup, telling Cool FM: “We were all shocked, this just came totally out of the blue.
DUP leader Sir Jeffrey Donaldson steps down after being charged with historical sex offences
“We called a meeting then first thing in the morning and all of us were kind of gobsmacked.”
Giving her support to Robinson, Little-Pengelly said: “I know many, many people are deeply shocked and devastated by this news, as I am.”
Robinson was a key ally of Donaldson and was fully behind his decision to back a Government deal on post-Brexit trading arrangements.
That saw the DUP end its two-year boycott of powersharing at Stormont and return to the Assembly and Executive in February.
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