It is potentially a felony to offer investment advice without being a registered investment adviser in the the State of Texas.
However, the statute of limitations is 5 years on this offense, so any potential criminal liability on your part is long past.
In regard to her personal claims, she could have potentially brought a fraud or negligence claim against you. However, the statute of limitations on these potential civil claims has also long past. Thus, she has no valid claim against you.
On your second question, her threats to expose embarrassing information about you unless you pay her money is criminal extortion
. You may report her to the police for this, and she could be arrested on felony attempt charges.
In regard to your question on libel, in Texas libel and slander are unified under the tort
. A claim for defamation only lies where the statement which is the subject of the defamation claim is untrue. Thus, the only portion of her threatened statement which could be defamation is that you "took advantage of her." Thus, you could potentially make a claim against her for defamation if she were to publish or state this false information to any third party. You can also sue her civilly for extortion under Texas law.
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