You can say

Je l’ai kidnappée

See the definition

Your assumption is wrong, Je lui ai enlevé means something like I removed (something) from him/her.

“I kidnapped her” can be translated by Je l’ai enlevée (note the final e).

Or, you could say something like “je l’ai prise en otage”. I took her hostage – note the “e” at the end of “pris”.

Another possibility is to use the verb “ravir”. You could say: “Je l’ai ravie”, which means exactly “Je l’ai kidnappée” оr “Je l’ai enlevée”.