She was there for 90 minutes on a layover, but as that doesn't require even a visa I would say NO.

https://www.msn.com/en-us/news/world/meghan-markle-and-prince-harrys-return-to-uk-for-christmas-ruled-out-after-king-charless-eviction/ar-AA1jNw14

@Fedor Agreed. To "enter" a country is different than to be physically present in it I also would say NO.