‘her’ in this example shouldn’t be capitalized. In fact, it’s too easy to identify the first word in these types of prompts when they have a capital letter. The word block could be all in lowercase but present the correct solution (in green bar) could still show the correct capitals for reference.
Agree but as a beginner it's a great help. Later on one has to type in answers anyway, without the help.
How do we know which version of 'you' to use. You could be speaking to anyone in this sentence!
In Duolingo, all versions of 'you' should be accepted. You can alternative between them for different sentences to practice conjugation.
In real life, chose the version based on who you are speaking to.
Is You are his mother accepted because one can refer to some respected person?