
Marrying into the Royal Family has changed the Princess of Wales’s life immensely and whilst she’s received so many special honours, she’s also lost a huge privilege she’ll never get back again. As she’s the future Queen Consort, it would be astounding to me if Kate continues to vote in UK elections and it’s likely she stopped exercising her right to do so in 2011.
Legally the Princess of Wales can vote, but it’s understood that she and her fellow royals choose not to do so. Speaking previously to TIME, Robert Blackburn, professor of constitutional law at King’s College London, explained that political neutrality is incredibly important to the Royal Family as a whole, not just the monarch.

"The King and active members of the Royal Family can legally cast a vote at general elections on the same basis as other eligible citizens, but in practice do not do so for obvious reasons, especially because it would cause a furore of media speculation and violate the constitutional requirement today that they maintain a strict party political impartiality," he explained.
Prince Harry has said in the past that he "[hasn’t] been able to vote in the UK [his] entire life" and he grew up just one place below Prince William in the royal line of succession. As the eldest son of the King and a future monarch himself, William no doubt refrains from voting too.
The Princess of Wales is one of the most senior royal women and likely follows his example of political impartiality and will continue to do so when she’s Queen.

This means she’ll never get to have her say in a general election again, though there were three of them that took place between the time she turned 18 (legal voting age in the UK) and the time she married Prince William in 2011 so at least she’ll have been able to do so then.
The change might have been an adjustment for Kate initially, though for those born into the Royal Family they have seemingly been raised with this focus on neutrality. The Princess of Wales has had to get to grips with a lot of royal traditions and protocols over the years and whilst the ‘no voting’ custom is a biggie, there’s many more unusual ones.
Whilst Kate probably wasn’t being regularly asked for autographs before her marriage, now she definitely can’t give them out to anyone. Members of the Royal Family aren’t supposed to sign autographs, apparently due to the security risk of their signatures being forged.

The Princess politely turned down requests for an autograph in the past when she attended the Chelsea Flower Show’s first ever Children’s Picnic. It was widely reported that some of the children asked her to sign their sketches and she responded, "I can’t write my name but I can draw" and did some drawings for the pupils instead.
When she was asked again about her name, the Princess explained, "My name's Catherine. I'm not allowed to write my signature, it's just one of those rules."
The only times we tend to see the Princess of Wales’s signature is in visitor’s books, like when she and Prince William had an audience with the new Archbishop of Canterbury, Sarah Mullally on 5th February. Instead of writing her name for people, Kate often spends a lot of time chatting or even participates in selfies which are just as personal as a keepsake.