Actually, neither is entirely correct. In Japan, her name is "ほろ” which in Standard Romaji would be rendered "Horo". Those japanese syllables that correspond to standard "r_" syllables have a sound that doesn't exactly exist in English. It uses a combination of "l", "r" and "d" mouth positions. I might write it in Katakana ... except that "Horo" is an Ainu word for "Wolf" and therefore not an import name.
Saying "Holo" wouldn't be too far off but less close than saying "Horo" while rolling the "r" a bit (and throwing a bit of "d" into it).
WRITING her name as "Holo" would be incorrect by Standard Romaji methods (there are no symbols for "L*"), but it certainly doesn't stop some people from doing so (including a certain Japanese graphic artist who didn't do so well in school methinks).
Conclusion is that you could certainly write "Holo" but you'd only confuse many people and make Japanese instructors glare at you.
How you *say* "ほろ” depends on how well you handle the last sound
Here's a specific counter-example or two: One of our posters uses the nickname "Risaa" "Ri-sa-a" (ﾘｻｱ) which is a Japanese interpretation of the English name "Lisa". My name, "Vexx" is a real trauma to try and Nihongo-fy as 3 of the four letters have no direct correspondence to the Japanese syllable list. (Be-ke-tsu???? ick!)