Botox for Neck Wrinkles and Masseter. Complaints of Difficulty in Talking and Chewing?

It's unlikely that it could be from Botox, unless alot ( >50  units ) were injected and deeply. If the symptoms don't resolve in 3-4 weeks, follow up with either the doctor that did the injection or a primary care physician.

Botox injected into the masseter muscles is intended to help atrophy the muscles by weakening them. The injections should be deep and carefully performed - if not, you can experience some unwanted side-effects, only until the product wears off.

There are recommendations if she is having symptoms related to swallowing.  For example she may benefit from having her bed put up on an angle at night, etc.  While the treatment will wear off, this is a highly disturbing situation.  Rather than going back to the treating doctor, I would advise she consults with her internist.  The internist might refer her to a neurologist or an emergency room physician with a special interest in toxicology.  There is not treatment to speed up the resolution of the symptoms.  Care is largely supportive until this happens.

Botox can be used on the masseter for hypertrophy and the neck for platysma bands.  If too much is used it may cause difficulty with masseter function ( chewing) and swallowing can be impacted if injected too deeply.

This has to do with the injections to the jaw muscles, and most likely not the neck muscles. Remember that injections in these areas are "off label" uses of Botox, and so there can be a wide variety in how these are performed, the number of units used, etc. When injecting anywhere near the mouth (which includes the jaw), it can affect speech, eating, chewing, drinking, and talking. Too many units or an incorrect placement on the left side is causing these issues for your aunt. It will go away with time, but there's nothing that can be done at this point.