I am not licensed in either Texas or Arkansas. Howerver, your mother needs an elder law attorney in Arkansas.
Powers of attorney or guardianships are only for the management of affairs while a person is still alive. Conversely, wills only become effective at death. You thus are correct that you being executor has no bearing on your relevancy to manage your mother's affairs for her while she is still alive.
You indicate that your mother's health is deteriorating. Niether I nor most ot the attorneys here are a medical doctor and cannot assetss your mother's mental capacity or competency. To the extent that your mother is mentally competent to handle her affairs, then your mother needs to execute a power of attorney,. While it would be better if this were drafted by an elder law attorney, if money is an issue, you can get a free financial and medical power of attorney and a living will for Arkansas at www.ilrg.com. You do not haev to purchase an already prepared form - simply copy and paste the form into a word processing document. Your mother will have to geet it signed and notarized. There may be other websites and I cannot vouch for a power of attorney from this site. Perhaps another attorney here will be licensed in Arkansas and can better advise you.
If your mother is not mentally competent, then you will need to find out the procedures to obtain a guardianship/conservatorship over your mother's person and property. Different states have different requirements and may have restrictions on whether an out of state person can serve. There are also bonding requirements. Again, an elder law attorney in Arkansaw can assist you with that.
Regardless of whether you get a power of attorney or guardianship, you need to keep absolutely pristine records. Keep your funds separate from the funds of your mother - no commingling. Keep track of every penny that you spend on your mother's behalf and document it. Keep receipts as well. I don't know if there are other siblings or famil members, but if there aree, invariably disputes arise between the person who has control overy your mother's property and anyone else. The best way to protect oneself is to keep good records so that you can rebut any claims of abuse of authority.
Know also that powers of attorney may be challenged. Anyone could try to take advantage of your mother by getting her to revoke a power of attorney or she may try to do it herself (many elderly citizens sometimes become convinced that their loved ones are out to take advantage of them when that is not the case). So, if she makes a power of attorney and tries to revoke it after she becomes mentally incompetent, then you have to bring a guardianship proceedings