Whatever model your sister finds herself considering, get her to check out the costs of inks BEFORE making her purchase!
e.g. I've just taken a look at one of the cheaper Canon models (TS3150), which is just £39.99 from PC World. However a single set of replacement cartridges from my favourite supplier (Inkredible) costs more than the printer itself, at a whopping £46.25! There have been two occasions on AB when I've successfully convinced people here to sell their almost brand new printers, and to buy something that's a lot cheaper to run, rather than to have to keep paying high prices to buy inks for a printer that they only bought a few weeks beforehand. It might well be best to try to avoid a similar situation for your sister!
I use a Canon Pixma MG5750 which, annoyingly, is currently showing as 'Out of Stock' on the PC World website. However it was priced at £59.99 and, given that it remains listed on their site, it might come back into stock at that price soon. If so, it would be well worth considering, as I only pay £13.80 for a full set of all five cartridges for it (with discounts available for bulk buying too).
Printers that use 5 (or even 6) cartridges almost invariably cost more to buy initially than those which use just 2 cartridges but the multi-cartridge models are usually FAR cheaper to run, with the savings cutting in from the very first time that replacement inks need to be purchased!