In a keynote speech, she will also call for reforms at Holyrood so there is a "Scottish Parliament with teeth" which is able to scrutinise and challenge the SNP government more effectively.
In her speech, she acknowledges that the SNP are now "odds on" to win the election on May 5.
She says that with Labour having had nine years without success, the Scottish Conservatives are the only party which can now fulfill the job of taking on the SNP.
She says the Scottish Conservative campaign will now focus on appealing to people who have never voted Conservative before.
She said: "You vote for me and I will do a specific job for you. I'll hold the SNP to account. I'll provide a strong opposition. And I'll say no to a second referendum – so we get the better government we deserve.
"My message is that – even if the people of Scotland don't choose to get rid of the SNP, your voice can still be heard."
She says that many people who never previously considered the Scottish Conservatives are now thinking about voting for the party.
"Perhaps they're even surprising themselves a bit in this. I wish I had a pound for every time I've heard somebody tell me: 'I can't believe I'm going to say this.'
"But we would be foolish to think we've sealed the deal and it's all in the bag. The truth is – many of these people are still thinking it over.
"If there's one thing I've learned about Scottish politics in the last five years, it's that people prize their vote pretty highly. So these folk – quite rightly – want to hear more about our plans.
"They want to know whether we're really up to the task. Making a shift to vote for us feels like a big step – I know that.
"So people are interested but –rightly – they are waiting for us to given them more reasons."
Next week's manifesto will set out Scottish Conservative plans to use opposition to demand the repeal of the Named Persons law, to back a sustainable NHS, and a better education system.
She also says that a stronger Scottish Conservative opposition will call for reforms to the way Holyrood operates.
She said: "The truth is that the Parliament itself isn't working as well as it should to help us do that job.
"What I want is to see a Parliament with real teeth in Scotland.
"I want to see Committees that are feared by Government, not patronised.
"I want Ministers to know that when they come to the Holyrood chamber or any one of the committee rooms they had better be prepared, or else.
"I don't think that means a second chamber. We have quite enough politicians in Scotland as it is.
"But we will push for a series of reforms.
"The conveners of key committees should be held by opposition parties to improve accountability.
"My opposition spokesmen and women should be able to question Ministers every week, not irregularly as now.
"And it's time we moved to a practice where – as far as possible - MSPs stay on a Committee for the full parliamentary term, so they know that this is their permanent job and responsibility."