If you mail a request for defensive driving, but were speeding to fast to be allowed to take, it can it possibly get accepted?

It is doubtful it will be accepted by mail. In person, you can attempt to convince the prosecutor or judge to allow it, though for that speed, I would doubt it very seriously.

If you are going 25 MPH over the posted speed limit or over 95 MPH in Texas, you are not able to take defensive driving. Your best bet is to ask the judge for deferred adjudication, though it will cost you more.

Your speed is too high by law to do a defensive driving class to dismiss your ticket. You should go to court to ask for deferred disposition to keep it off of your record. The judge/prosecutor may require you to do defensive driving class and/or community service as a condition of deferred disposition, if granted. In texas, deferred disposition is completely discretionary and the judge/prosecutor do not have to offer it. If you are unable to drive to that court, you should hire a traffic attorney to go for you. If you are ultimately convicted, you should quickly consult with an attorney (you only have 10 days) to see if you can appeal your case to a county court, where they may offer deferred dispostition (you can easily appeal if the court is not a court of record, but it is much more difficult if the court is a court of record).