All that 1p Mobile are really saying is that you need to top up the phone with a tenner's worth of credit every 4 months but, to save you forgetting to do it the first couple of times, you can pay three lots of £10 (=£30) all at once, so that the credit will last for 12 months instead. (In my opinion, that actually makes it more likely that you'll forget to top it up at the end of the 12 months!).
1p per minute might not sound much but if, say, your neighbours uses the phone a few times to call her GP's surgery, and gets stuck in an hour long queue each time, her credit could get used up surprisingly quickly. There's also the risk that she might forget to top up the phone just before she needs it for something really important.
If she can afford it, I'd suggest that she should pay a fiver per month (which isn't really a lot for peace of mind) to one of the phone providers that offers unlimited UK calls for that amount as part of a 'bundle', with things set up so that the fiver is automatically taken from her bank account each month. Then
(a) she won't have to worry about whether her phone is topped up or not ; and
(b) as well as having the phone available in emergencies, she'll be able to natter on for hours to her sister in Plymouth, her daughter in Edinburgh and her old school friend in Swansea without paying a penny more to do so.
This thread, from yesterday, might be relevant here:
https://www.theanswerbank.co.uk/Technology/Question1828277.html