@BeanieTeen You said: 'Aren’t people a bit embarrassed to get so confused over how their first and often only language works? It always surprises me how quick people are to admit they don’t understand how to substitute ‘they’ for ‘she’ in a sentence.'
People get grammatical structures wrong all the time - in fact there are several structures that are frequently applied incorrectly. It is OK to ask how they should be used.
In this case - for most of the last 100 years, the literary and common usage of the male and female pronouns - he / she / they for subject pronouns and him / her / them for object pronouns and his / her's / their's for possessive pronouns applied to singular male / singular female and plural subjects, where male / female referred to the distinction between the sex classes, between those which are is on the developmental pathway to being capable of producing small gamets (males) and that which is on the developmental pathway to producing large gamets (females).
Recently - and it is very recently, there is a movement towards using the words male and female, the words man and woman and their associated pronouns to mean identifying with a set of gender based stereotypes, or a set of internally defined feelings that a person associates with one or other of the words previously used to define the sex classes, male / female and their associated nouns man / woman and to introduce a third concept of non binary humans that identify as neither.
We have become accustomed to seeing he/him, she/her and they/them as shorthand to help us identify people who wish to have these specific pronouns used when referring to them, especially where the previously held conventions do not apply, or in solidarity to those who feel that the conventionally applied pronouns do not apply to them.
The use of he/they and she/they, deviates from this new convention as it proposes two alternatives for the subject pronouns rather than proposing subject and object pronouns but does not define the circumstances under which one should apply he rather than they and likewise she rather than they.
Much of how we use language comes from observing the behaviour of others and from reading, watching and listening to narratives and this use of language becomes reflexive if not entirely instinctive, so we have learned to use he / she / them in the situations where we have seen, heard or read their use the past. To over ride these reflexes / instincts (I use that word cautiously as it see it more reflexive than instinctive) we need to consciously relearn how to apply the rules in new situations and on an individual basis, similar to the way we learn the names of new people when we meet them, however, now we need to learn additional pieces of information for some people and apply our reflexive learned responses to others.
This is similar to how adults learn second and subsequent languages compared to how children acquire language. Typical adult language learning uses a translation of our existing words to the new language whereas typical childhood language acquisition assigns a word in the language to the object, subject, concept that is being learnt.
You might be embarrassed to ask.. but it is better to ask than to continue in confusion.