i will suggest u find model thats with well known good keyboard, such as Lenovo Arccutype , Asus chiclet keyboard

In terms of spec, your mum don't need powerful CPU nor GPU. i3 (can even get by with Celeron ) with Intel IGPU is more than sufficient.
Also don't need lots of RAM, 4GB is sufficient, unless she open up lots of tab when she surf net.

Since she is going to type a lot, a laptop with good keyboard is very important. Unfortunately, keyboard preference is kind of subjective. Generally, Lenovo / Sony / MacBook has keyboard that are well like. Ask your mum to type on a few models to find her preference.

Laptop with bigger screen tend to be heavier. So you may want to consider the trade-off between larger text on screen vs mobility.

Since she may look at screen (a rather static one as well) for long period of time, may want to consider whether she will like model spec with matte screen.

SSD is a worthwhile consideration as it make laptop more responsive (besides all the other benefits over HDD). 128G ~ RM300, 256G ~ RM600.

Samsung
Book 9 Lite NP905S3G-K01MY, AMD A6-1450 + AMD HD8250 + 128GB SSD@RM1999[1.58kg], 4GB, W8
This is an interesting model. Except for a big screen (only 13"), it is quite ideal for your mum.
Price is RSP, negotiable.

Alternatively, instead of buying new, may be can scour the garage sales threads and look for 2nd hand MacBook Air 13" (2011 or later). Lots of writers live with MBA

root for macbook air... the thing most important for writer to choose laptop is

1. godly keyboard = typing a lot, type on it already worth back the price...
2. portable = can carry around anywhere to write.. different environment different mood right?
3. good battery life = write anywhere they like even without the adapter...

even JK Rowling used macbook air... but her price is 1 words at least USD 1000...