An attempt by the Lords to force the Tories to honour their manifesto pledge to retain the triple-lock formula when calculating pension increases was defeated in the Commons last night, and Morris voted to scrap the triple-lock. Remember that folks when she comes begging for your vote at the next election.
I doubt it was a three-line whip as 46 Tories didn't vote last night. In any case, plenty of MPs go against the whip if their conscience dictates that.
According to this there was a three line whip https://metro.co.uk/2021/11/16/millions-of-pensioners-to-lose-out-as-mps-vote-to-scrap-triple-lock-15608051/
She could always have rebelled or found an excuse/reason not to be there.
And she's defied the whip before.
On 15 November 2018 she submitted a letter of no confidence in Theresa May's leadership. In October 2020, Morris was one of five Conservative MPs who broke the whip to vote for a Labour opposition day motion to extend the provision of free school meals during school holidays until Easter 2021.