This is the first time such a question is asked to me, so I am very pleased to answer something new, for a change!
I picked that icon (don't remember where from) - before I joined Duolingo as a learner, actually - because I immediately felt it was a good symbol of who I believe I am in life.
And eventually, now, you have expressed what I feel about my role here. Thank you for paying attention, I will try to remain up to your vision...
"Elle voit qu'il l'aime": I have found 7 possible interpretations...
Marie voit que Pierre aime Marie = she sees that he loves her (herself)
Marie voit que Pierre aime Julia = she sees that he loves her (another woman)
Marie voit que Pierre aime Paul = she sees that he loves him (a man)
Marie voit que Pierre aime le chien = she sees that he likes/loves it (a masculine animal)
Marie voit que Pierre aime la girafe = she sees that he likes it (a feminine animal - no pet)
Marie voit que Pierre aime le vin = she sees that he likes it (a masculine thing)
Marie voit que Pierre aime la fleur = she sees that he likes it (a feminine thing)
For English speakers it is troublesome to deal with pronouns and their various forms in French where they are not required in English. From the French perspective the opposite is true. They ask how to be sure what is intended if stressed pronouns are not used. (Just to mention one example)
A. Subject pronouns - These are: Je ( = I), Tu ( = you), Il/Elle/On ( = He/She/We or One; informal), Nous ( = We), Vous ( = You formal or You all) and Ils/Elles ( = They).
These are the ONLY pronouns that replace SUBJECT NOUNS.
B. Tonic pronouns - these are: Moi ( = Me), Toi ( = You), Lui/Elle ( = Him/Her), Nous ( = Us), Vous ( = You; formal), Eux/Elles ( = Them)
These only replace OBJECT NOUNS preceded by a preposition.
C. "En" pronoun - This replaces OBJECT NOUNS that are:
Countable objects preceded by un, une, deux, trois etc
Uncountable objects but of specified quantity - preceded by "de" or " d' " e.g. un sac de, une tasse de, un verre de, une bouteille de etc
Uncountable but of unspecified quantity - by using the partitive articles of "Du", "De la", " De l' " and also plural number of countable objects preceded by "Des"
- Tonic (stressed/disjunctive) pronouns can also be subjects: "toi et moi sommes amis" = you and me are friends.
- Direct object pronouns are: me, te, le (il), la (elle), nous, vous, les (ils/elles)
- Reflexive pronouns are: me, te, se (il/elle), nous, vous, se (ils/elles)
- Indirect object pronouns (verbs constructed with the preposition "à") are: me, te, lui (il/elle), nous, vous, leur (ils/elles)
It is a matter of interpretation about who or what is "il" and who or what it "l' ". So there are a lot of variants, that I have just checked.
Note: only "he loves him" or "he loves her" or "he loves it (pet)" are correct interpretations of "il l'aime". Maybe also if "il" is a pet loving someone, we could get "it loves him/her".
I put "She sees that he loves her", thinking that when aimer is used with a person, it always means "love" rather than "like", but I was corrected to "she sees that he likes her". Why doesn't aimer mean "to love" if we assume that the l' refers to a "she" instead of an "it"?
I wrote Elle voit qu'ils l'aiment. I don't know what I had in mind - perhaps parents' love for a child - but I can't see what is wrong with my sentence. Anyone else try this? Unsuccessfully, I might add. It got dinged.
And it won't let me suggest that "my answer should be accepted".
Why wasn't "She sees he likes her" incorrect?
"Aime" also means likes as well as loves.
Also, in English, a lot of people unnecessarily put the word "that" throughout their sentences and it appears the people who programmed Duolingo's AI also do this, hence didn't add my answer as one of the acceptable responses as a result