This is she considers it fair despite the stock's 25 per cent rise since her bid almost three weeks ago, a source said.
The source close to dos Santos said the offer by her Terra Peregrin company - which values the whole Portugal Telecom holding company at 1.21 billion euros (1.51 billion US dollars) - already incorporates a premium to shareholders.
The holding company has no operating assets but owns a near 26 per cent stake in Brazil's Oi, which has incorporated PT's operating assets after a merger that is still to be fully completed. It also holds 900 million euros in debt issued by a bankrupt holding firm of Portugal's Espirito Santo Group.
Dos Santos launched the bid for Portugal Telecom on 9 November in an attempt to thwart a separate 7.025 billion-euro bid for PT's operational assets by Altice, controlled by Franco-Israeli billionaire telecoms entrepreneur Patrick Drahi.
On 12 November, private equity firms Bain Capital and Apax Partners joined the bidding battle to buy the operating assets from Oi, launching a bid worth 7.075 billion euros. Portuguese conglomerate Semapa joined the funds on Thursday, expecting to take a five to 10 per cent share in the investment.
Oi said it had not received any improved bids so far.
Several analysts have said that the price offered by dos Santos is too low and the most likely scenario was that Oi would sell the Portuguese assets unimpeded.
The entry of a Portuguese partner would help address concerns in Portugal that one of the country's largest companies and employers will no longer be Portuguese.
Dos Santos, the daughter of Angola's president Jose Eduardo Dos Santos, has said her bid was designed to preserve the company as a single Portuguese company.
The bid represented a 17 per cent premium over the three-week average market price of the shares before it was launched, but PT shares have risen more than 25 per cent since the bid to trade at over 1.5 euros.
Shares were flat at 1.55 euros in early trading on Thursday, while Semapa was 2.1 per cent lower at 9.1 euros.