Sorry, no experience of PCP (always buy old cars outright), but bear in mind that the more expensive the car, the dearer the insurance - so you end up having to pay extra twice over. Personally, I'd go for a runaround, but not a really cheap one, if you're able. If you pay £2-£3K, you're likely to be able to get something decent, but once you're heading down towards (or sub) £1K, that's when lemon-hood frequently kicks in - you may get lucky, but you may not.
To get an idea of what car insurance premiums you may be looking at, have a look on Autotrader/eBay or wherever, find the closest match to models you're considering (same engine size, power, age etc) that you can (that have a photo showing the number plate); then go to GoCompare or CompareThe Market and go to 'get a quote'. It's all automated and the quotes appear on screen at the end - you don't have to 'make contact' as it were or speak to anybody.
Put a line of zeroes for your phone number; you don't even have to give the exact info at this stage if you're concerned. Feel free to amend her name, house number, date of birth by a few days if you prefer - it's only a general quote-finding exercise at this stage. Just don't change anything significant, otherwise your result could vastly differ! Pay attention to the 'occupation' field - obviously, don't lie, but try different options from the drop-down menu that could legitimately apply to her situation, as this can heavily skew it. e.g. don't put unemployed if she's not actively seeking work just yet; we also found that certain descriptions can trigger panic when wording the same thing slightly differently (e.g. 'Research scientist' can give them the vapours that you might possibly work in a vivisectionist facility and thus could become a target for violent/dangerous animal rights activists - when you might 'just' work in an NHS hospital lab).
Once you have a registration number of a comparable car that you're considering, just use that and it will ask you 'date you bought it' OR 'not yet bought'/'considering purchasing'. Obviously tick the second one. You're doing nothing at all untoward or unusual by researching how much the insurance element of a car would cost you, were you to buy it, any more than you are by looking online for actual purchase prices in the first place.