I think I would wait a couple of years, not because it it's unsuitable as such but she'd appreciate it more if she were a little older.
The website says "The Lion King is recommended for a general audience. As an advisory to adults who might bring young people, Disney recommends The Lion King for ages 6 and up. Children under the age of 3 will not be admitted into the theatre. All persons entering the theatre, regardless of age, must have a ticket."
I phoned up the box office in Bradford about this for my little girl, who will be four and a half by the time we see it next year and was told that Disney do not recommend the show for children under six and consequently, there are no child concessions!
I took my much older kids recently to a matinee (travel time from home meant an evening show was out of the question) and there were lots of small children who were transfixed for the first half and really bored in the second. Lots of bathroom trips, lots of loud moaning "is it nearly finished" - I was staggered by how many small children were there given the price of the seats. I would say under 6 = just not worth it - and not very fair on the rest of the audience, because they have to endure all these bored small children - quite naturally, they didn't just sit there thinking "I'm bored"!