If your attorney never entered an appearance on your behalf -- never filed any paperwork for you, never attended a court hearing, had literally no contact at all with the justice court or its staff -- then there is no attorney-of-record relationship that would require court approval to change or end.
You may have other rights and remedies if your attorney's withdrawal is without your consent, but what those rights and remedies are, and how much practical leverage they may give you, depend very much on the terms of the engagement (which typically are spelled out in an engagement letter or representation agreement) and the circumstances of the withdrawal. There are some circumstances, for example, in which an attorney may be ethically compelled to withdraw, regardless of his own or his client's preferences. More common grounds for withdrawal are for nonpayment of fees or expenses, or a refusal of the client to cooperate or follow the attorney's advice, or for a serious and un-fixable breakdown in communications.
Also, things may be more complicated if your attorney took your case on a contingent fee basis. If so, he or she may have also acquired an interest in your potential winnings (either through settlement or trial) -- and that interest isn't necessarily ended just because you've discharged the attorney. I've linked below a guide that I wrote a few years ago here on Avvo regarding how to go about firing your contingent-fee lawyer. There are some important pitfalls that you need to look into before you act.
If you're hiring new counsel, he or she may well be able to also advise you on what your and your withdrawing/former lawyer's respective rights and obligations are. To do that, he or she would need to review carefully not only your contract with your withdrawing/former lawyer, but also to consider all the other circumstances.
Finally, the State Bar of Texas investigates and prosecutes professional misconduct committed by Texas attorneys. Not every complaint against or dispute with a lawyer involves professional misconduct, and especially if it involves an attorney's withdrawal that hasn't hurt the client's legal position, an attorney's decision to withdraw would only very, very rarely be considered professional misconduct. Certainly nothing in your question is enough to show professional misconduct, and unless your withdrawing/former attorney has committed professional misconduct, the Bar isn't going to be eager to get in the middle of your relationship. Nevertheless, if you and your withdrawing/former attorney can't reach agreement regarding how this ought to be resolved, then as a last resort, the State Bar’s Office of Chief Disciplinary Counsel (toll-free at 1-800-932-1900) can provide you with information about how to file a complaint.
Mr. Dyers answer covers the issue well. Two more points that may apply depending on the circumstances: Even if your attorney has had no contact with the court, she must protect your interests in the suit. So if there is a deadline coming up that you could not meet without help, the lawyer has a duty to take care of that before withdrawing, whether it be an actual response to whatever is pending or getting it put off until you can find another lawyer. Also, if the lawyer has been paid a fee, she may be required to return some of it depending on what she has done so far.
This is not legal advice. You should always discuss the specifics of your issue in person with an attorney. Be aware that there are time limits on all claims that depend on the kind of claim, so do not delay in seeking an attorney.