Emma Harrison, founder of training firm A4e which had offices on Queen Street, Sheffield, is pleading to be allowed to keep the developments at 12th century Grade II-listed Thornbridge Hall near Bakewell.
A public inquiry is scheduled for October.
If she loses, everything will have to be removed and the land restored to its former condition within six months.
Ms Harrison lives at the hall with husband Jim, who is boss of Thornbridge Brewery.
She did not respond to a request for a comment on the planning battle, but has been appealing for support from visitors and residents.
In Under The Edge parish magazine last year she wrote they spent their savings on a drive and cafe so the hall could remain open to the public.
They had presented the plan to the Peak Park in March 2020 - who were ‘encouraging’ - just before the first lockdown.
She claims the offices were then ‘barricaded’ and no one answered the phones. And after months of ‘silence’ they decided to go ahead with the works so Thornbridge could ‘survive’.
The development includes Quackers Cafe, a 100-space car park and a quarter-of-a-mile long road.
When the Peak Park issued an enforcement notice she urged people to support them due to the ‘immense benefit Thornbridge brings to the people, the area and the UK’.
It had also created jobs, with numbers up to 26 last summer ‘and climbing!’
And she had a dig at Peak Park planners, stating they had ‘never seen and don’t want to see’ the plans.
She added: “We have no idea why; people tell us that it seems mean and spiteful and driven by jealousy.”
Ms Harrison successfully appealed against the enforcement notice and a public inquiry will be held from October 11-14.
The Peak District National Park Authority says the estate has several listed buildings, a registered park and garden and is in a conservation area. As a result it is ‘a particularly sensitive location’.
The new works ‘cause significant harm to the heritage assets’ and ‘possible damage to trees, habitats and archaeology’.
And where a conflict exists between conservation and public enjoyment within a national park, ‘conservation interest must take priority’.
During the pandemic the offices were closed and pre-application advice was restricted to ‘priority’ applications such as major developments and listed building consents, which was ‘clearly stated’ on the authority’s website, it added.
In a statement, the Peak Park said: ‘As there was no opportunity to assess the impact on this sensitive site and location as a starting point prior to the works being undertaken, the authority has asked that all relevant aspects of the development are removed and the land restored in accordance with the enforcement notice’.
Ms Harrison quit as boss of A4e in 2012 just a day after she gave up her role as ‘back-to-work’ adviser to then prime minister David Cameron, following a police probe into the firm.
As part of its work, A4e, which employed 3,500, handled millions of pounds worth of government contracts for welfare-to-work schemes.