If it is a large tech company the CEO likely does not even read his or her own email. CEOs of large companies do not have the time to look through their own email so typically a secretary of some kind screens the email separating out actual business email from everything else. This includes but is not limited to:
- People trying to get hired by directly asking the CEO
- People's parents trying to get their son or daughter hired
- Crazy emails that make no sense
- Spam that made it past the filters
- Phishing and spear phishing attacks
- Death Threats
So it is highly unlikely that the CEO of the company would ever even get to see any email from your mother. She likely will get a nice precanned email thanking her for her email. Worst case is the email redirects her to HR or Ethics and they take her email seriously and investigate it. If the tech company is a good company they will get your side of the story before making any decisions, at which point you can diffuse the situation by giving a short and simple explanation like you did in the opening question.
However, despite this specific threat not likely going to materialize into anything meaningful, she can still try and try again using different avenues of attack. As a result you will need to make sure your mother does not get information like your hiring manager's contact information. If you have a chance in casual conversation with your hiring manager either between interviews or after you are hired, make mention that your mom opposed your decision. This can preemptively diffuse a situation before it had a chance to form.
Another aspect is stalling your mother until after you are hired, since she may give up after you have quit the PhD program. For example: asking your mom to give you some time to do some research on the company. Like checking to see if the company will help pay for PhDs since you may be able to sooth your mother's concerns by telling her this and that even though you are changing paths away from a PhD that there is still a possibility in the future that you can go back to it.
The ideal solution (if possible) is to go to the source and do everything you can to get your mom to trust you and let you make your own decisions (see Caleb's answer).
And one last random thing, which goes without saying: Whatever you do, do not quit your PhD until after you have a confirmed offer.