The OP's solution “She has been banned from tennis for three years.” is grammatical but means the length of the ban lasts three years, it does not suggest that there are another two more years to go.
It's been three years since she was given a five-year ban in 2018
The five-year ban was (hypothetically) issued in 2018, so the decision is a finished action. The ban; however, is still ongoing which we can express by using the present perfect.
Three years have passed since she was banned from tennis for five years.
The first clause uses the present perfect while the subordinate clause is in the simple past passive.
She hasn't played tennis since being banned for five years in 2018.
The expression "being banned" is in the present continuous passive, I feel it gives a better sense of the ongoing nature of the current ban than using the past simple passive "was banned", not everyone will agree.
Some examples taken from the net
- Face Recognition Is Being Banned—but It’s Still Everywhere (Wired.com)
- Rep. Marjorie Taylor Greene Is Back On Twitter Despite Being Banned And Urging GOP Boycott (News Yahoo!.com)
(capital letters are used because they are titles of magazine articles)
But there’s another, more conceptual debate that transcends partisan politics and carries implications beyond Trump’s freedom to tweet. It’s the question of whether the largest social media companies have become so critical to public debate that being banned or blacklisted by them — whether you’re an elected official, a dissident, or even just a private citizen who runs afoul of their content policies — amounts to a form of modern-day censorship. (Washington Post)