Your goal is fine, fully appropriate.
Of course your mom should be able to use it;
anyone who can type and read should be able
to use it. Fine. And there is no need
for any nonsense gibberish such as
"RT, MT".

But, I believe you are over estimating the importance
of having some natural language understanding,
under estimating the difficulty of achieving that
understanding reliably in software,
and are very much under estimating how easy
to use, even for your mother, for anyone
who can type, something like I outlined can be.

E.g., when I was in grad school, I took out some
time to earn some money so that my wife and I
could complete our Ph.D. degrees. For the money,
I worked as an applied mathematician, computer
guy in a research shop doing work mostly for
the US Navy. So, yes, we had secretaries who
did a lot of typing but had no word processing.

As part of my work in applied math, I ended up
as system administrator of a super-mini computer.
Of course, for programming, it had a text editor.
If only for writing the computer manuals, it
had a simple text formatting program, call it
a member of the family of Runoff programs.
And I'd gotten a daisy wheel printer nicely
driven -- asynchronous serial communications
with ASCII characters and the XON/XOFF
handshaking (pacing)
protocol -- by
the computer. So, we were GO to do a LOT of
typing.

Soon enough the secretaries wanted to get on
board with this new stuff. So,
for them, one at a time, we pulled
some 5 conductor, general purpose
signal cable with a 25 pin plug at each
end (we only connected the pins for the
signals
SEND, RECEIVE, and
SIGNAL GROUND), and a dumb terminal.

Bottom line: All the secretaries got
on board right away. The ones without
a terminal begged for one. No one
ever gave one of the secretaries more than
a few minutes of 'training'. They all caught
on right away, to logon, files, the hierarchical
file system, the text editor, the runoff program,
the daisy wheel printer, etc. Right away.

Later as a college prof, I did the same
for the business school, and again the
secretaries 'got it' right away.

Gee, we weren't asking them to write
macros in TeX!

So, back to my suggestion:

You want an appointment. So, you send something
like

=== May we meet? Let's pick a time and place.

=== My name

=== My job

=== My e-mail address

=== My phone number

=== Subject of meeting

=== When to meet

=== Where to meet

or some such. Then you use just typing to
insert data
under each of these or some such,
likely need something better, but you
get the idea, and send your e-mail.

A human, including your mother, can read it
and respond. And they can respond with a
similar e-mail.

If either end of the communications is using
your software, then the software can
read that data and make sense of it
much easier than for natural language processing.

Or, send the person some e-mail with a URL
to a server with a Web page with a form and
some JavaScript to help the person fill out
the form. Then we're into just
a Web form solution that we know very well
how to handle.

Forms work great; people are really good
at entering data into forms.

For people who have your app, it can replace
the Web site.

No way do you have to use gibberish such as
"RT, MT". Instead, everything a user reads
can be in complete English sentences with
a button with Help for more explanations, etc.
It can be easier to use than most Web forms,
and 1+ billion people use those.
It can be easier to use than Google,
e.g., where Google has those little horizontal
bars to indicate (I never got that memo or
read any explanation in a help message)
for more options. Last I checked, Google
had a lot of users.
It can be easier to
use than the Amazon Web site, easier to use
than Facebook.

You are underestimating
the ability of your target users to
make use of simple computer user interfaces.

My guess is that there is no way natural language
processing can be good enough
that, net, it is easier to use than
just some simple forms or something like
I outlined above.

Gibberish like "RT, MT" is really a straw man to
knock down. Instead, never but never should
there ever be any gibberish or undefined terminology
or undefined acronyms in any user interface. That
rule is easy to obey, and natural language processing
is a very hard way to obey it.

The real business need and opportunity is
meeting scheduling, not finding
work for natural language processing.