Good suggestions in the thread about running ethernet or extending the coax. Other options:

https://www.amazon.com/Introducing-eero-mesh-WiFi-system-3-pack-/dp/B07WMLPSRL

https://www.amazon.com/Google-Wifi-System-Router-Replacement/dp/B08GG9CMLR/

Eero just released the new wifi 6 models, but I think the previous ones are great. You can get a good deal on a previous model three pack right now.

https://www.amazon.com/Introducing-eero-mesh-WiFi-system-3-pack-/dp/B07WMLPSRL/

I have a mix of the previous model regular and pro models in my house and the wifi is great. I'm a pretty heavy user and the pros are probably more than I need. I've since recommended the regular ones to people and they work great.

The easiest and most reliable thing to do would be to get something like an eero mesh. The eero is self configuring and self adjusting. Leave the main verizon router in place and disable the wifi. Add the first eero and put it in bridge mode and connect it to the verizon router. Make a new ssid for her and tell her it's the new wifi. Add the other two wherever it makes sense to. If there are any issues, just move or add one. You can even manage her setup remotely if you want.

https://www.amazon.com/Introducing-eero-mesh-WiFi-system-3-pack-/dp/B07WMLPSRL/

Get a mesh router, or ethernet to coax moca converter.

The first option is the much better one. Extenders are garbage.

Get one of these:

https://www.amazon.com/Google-WiFi-system-3-Pack-replacement/dp/B01MAW2294/ref=sr_1_3?dchild=1&keywords=google+home+wifi&qid=1586059538&s=electronics&sr=1-3

https://www.amazon.com/AmpliFi-Ubiquiti-Seamless-Wireless-Extenders/dp/B01L9O07FS/ref=sr_1_2?dchild=1&keywords=amplifi&qid=1586059554&s=electronics&sr=1-2&th=1

https://www.amazon.com/NETGEAR-Orbi-Ultra-Performance-Whole-System/dp/B01K4CZOBS/ref=sr_1_3?dchild=1&keywords=netgear+orbi&qid=1586059581&s=electronics&sr=1-3

https://www.amazon.com/Introducing-eero-mesh-WiFi-system-3-pack-/dp/B07WMLPSRL/ref=sr_1_3?dchild=1&keywords=amazon+eero&qid=1586059594&s=electronics&sr=1-3

Moca works by operating at frequencies on the coax that do not interfere with the cable company signal. It does not actually come from spectrum, it is a capability of equipment. So grab the current 3.1 modem from spectrum, then buy any of the routers i listed and youll be set.

To put it simply it is a router that comes in multiple pieces. You plug the actual router (main piece) into your modem so you get internet, and then place the other pieces (access points) strategically so that they hop off of each other and they all form one massive network.

https://www.amazon.com/Google-WiFi-system-3-Pack-replacement/dp/B01MAW2294/ref=sr_1_3?dchild=1&keywords=google+home+wifi&qid=1587266105&sr=8-3

https://www.amazon.com/Introducing-eero-mesh-WiFi-system-3-pack-/dp/B07WMLPSRL/ref=sr_1_3?dchild=1&keywords=amazon+eero&qid=1587266242&sr=8-3

https://www.amazon.com/NETGEAR-Orbi-Whole-Home-System/dp/B07CQDHPFT/ref=sr_1_3?dchild=1&keywords=netgear+orbi&qid=1587266257&sr=8-3

https://www.amazon.com/AmpliFi-Ubiquiti-Seamless-Wireless-Extenders/dp/B07KTQKLW2/ref=sr_1_1_sspa?dchild=1&keywords=ubiquiti+amplifi&qid=1587266273&sr=8-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExQklIS1kyU1JOVFVHJmVuY3J5cHRlZElkPUEwODg5MjI0RVFOVVRXTUMzRksmZW5jcnlwdGVkQWRJZD1BMDIxNzE4NDI0TUI3VTYzQTdaMzYmd2lkZ2V0TmFtZT1zcF9hdGYmYWN0aW9uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl

Wherever you are gaming, make sure you use an ethernet cord and not wifi. You may be able to get away with wifi gaming for a bit, but you will experience lag/latency issues/disconnect at some point. Seriously networking your house takes an investment.

I would recommend the TP-Link WiFi 6 Router AX1800. I currently use it and it has very fast speeds, great range, and several features include QoS and WPA3.

EDIT: However, if your main concern is range, I would recommend a mesh wifi system like the eero mesh WiFi system.