In theory you should not need defleeing treaatment. Having said that I looked after my neighbour's house cat while she was away and found it to be full of fleas so it can happen. Just inspect the cat's coat regularly. Worming treatment would be advisable
laptopsteve, ignore kitesurfer - full of bulls**t! I agree with LottieAnne, in theory you shouldn't need to de-flea or worm your cat, but just keep a watch in case - fleas can come in in various ways, not just on the cat!! As for worming, if mog isn't going out and catching anything, she shouldn't get worms as they get them from their prey. But watch her anyway and if you spot any fleas or worms, just treat her then. I wouldn't bother with prophylactic treatment, though.
An excellent deflea-er is Stronghold, bought from your vet and is a spot on treatment on the back of the cats neck. It also worms them (round worms only not tapworms) is cheaper and IMO is better than Frontline. One of my cats had a really bad reaction to Frontline so have stopped using it, but use Stronghold on both my dogs and cats, its brilliant.