Translation:They admire her.
The lu- prefix indicates that there is a third person singular object, i.e. "him", "her", or "it". The Klingon sentence does not actually make it clear which is meant. Klingons are fine with that ambiguity, but in English you have to pick one. Which one the speaker intends will usually be clear from context, but since Duolingo does not provide context, you just have to randomly pick one. When showing you the "best" answer Duolingo also randomly picks one, so sometimes it might say "him" or "it". When you are entering your translation it will accept any of the three options as correct.
So are you saying that when you type in the answer it will accept They admire? However when you do the clicking of the words since it has the word HER in the options if you don't click HER as in They admire her then it will mark you wrong? I didn't put the her and got it wrong when I did the click answers so was just wondering if that what the difference is
No. The software will never accept "they admire" as a translation for luHo'. The lu- prefix indicates that there is a third person singular object. The exercises based on this sentence will accept, "they admire him," "they admire her," or, "they admire it." If you are given a tile based exercises you may only have the tiles for building one of those options. Sometimes you might have tiles available that will let you choose between the options, but most of the time you will only have the tiles for one option. However, the software should ALWAYS offer you at least one of "him", "her", or "it". And if you do not select at least one of those, it will, indeed, be incorrect because the lu- prefix tells us that it must have a grammatical object.