home wireless to AT&T landline

Are you saying she has a Verizon wireless home phone LVP2? She wants to change it to an AT&T landline, why? If you want to port the number from one service to another you don't cancel the old service until the port is competed to the new service. If she has a Verizon wireless home phone and has a good cell signal, I sure wouldn't change to a landline, anybody's landline. I've had one for years and have been very happy with it, but you do need a good signal. If she has an older version of Verizon wireless home phone that quit working because of the change to HD LTE get the newer version (LVP2). 

As spoom2 says, do not cancel the old service if you want to keep the number!  Order the new service with the request to port the number from the old provider giving the security information necessary for the old provider account.  Your new service provider will contact the old provider and port the number.  The port should terminate your old service, but follow up afterwards with the old provider to be sure they're not still billing you for nothing.  The port from the old provider to the new shouldn't leave her without phone service for more than an hour or two.

AT&T makes ordering land lines hard and expensive.  Expect to pay more than $50/month.  You might want to seriously consider keeping the Verizon Wireless Home Phone. 

Alternately, you could try Ooma's Telo LTE service.  For under $30 a month, you get a box that communicates to the T-mobile wireless data network for making calls that you connect a regular phone to.  Ooma also has a VOIP service that would work on a wired Internet connection, but I'm guessing you don't have one of those there.

Another option to consider, there are cordless phone bases that will use a cell phone to make and receive calls.   So, you buy one of them and order a cell phone with service.  Connect the cell phone to power and the cordless phone base to the cell phone.  You then just use the cordless phone as you would any home phone.  I'm worried that number dialing may be "different," though, and that may be a show stopper.  A Wireless Home Phone device should be better.  AT&T used to sell WHP, but they want to sell Wireless Home Internet now, instead.  T-mobile seems pretty much the same as AT&T, here.

@JefferMC Good info. I wasn't aware Ooma made a wireless home phone, there's others also. With the direction being taken by the phone companies on traditional landlines I'd sure go that route rather than arguing with them about POTS service. The only thing I like to stress is the need for a good strong cell signal for reliable service.  

I purchased the prior Ooma Wireless device which has recently been upgraded (by them, free of charge) due to the shutdown of the Sprint network.  I have used it both on the T-mobile network and my Wired Internet. But if you don't have good wireless access, the base device (without the Mobile radio USB stick) is cheaper, and so is the monthly service (but requires other Internet, of course).  Oh, you also get a <sarcasm> whopping </sarcasm> 1 GB of "free" Internet access a month, and additional GBs are "only $8.99 / GB" [their words].