With her partner pushing her in a wheelchair, Markle was said to have refused to leave the palace area and went on to buy souvenirs, including masks of the duchess and Prince Harry.
In May Thomas Markle sparked a whirlwind of media attention after being exposed for selling pictures to paparazzi before the royal wedding and then giving a tell-all interview to British TV.
Meghan's half-sister flew to the U.K.at the end of September with the aim of confronting the Duchess about her relationship with their father.
On Sunday, Samantha teased her Twitter followers, writing, "Everybody would love to know what's in that letter".
"I've always wanted to see London, but really I wanted to make the trip and sort of speak the wishes and thoughts and sentiments of my father, and hopefully get a message to my sister", Samantha said on Britain's Channel 5 last week.
Samantha has been demanding a meeting with the Duchess of Sussex and her husband since she was snubbed from the royal wedding in May.
Meghan Markle's half-sister, Samantha, has been royally denied.
"She explained she had been in touch with palace officials and claimed they had ignored her advances, leaving her no choice but to arrive uninvited".
However, as eyewitnesses told, she could pass a note to sister (if it came to the recipient, is unknown), the contents of which, of course, curious to many.
While in the United Kingdom, she also sat down for an interview with TV personality and journalist Jeremy Vine where she discussed her view on the volatile situation.
"I just think that families can be this way when there's confusion and when people are hurt", she added.